SAN DIEGO -- As of Saturday, Cubs pitcher Matt Garza fully expected to make his start Tuesday night. Now, it's not certain whether the right-hander will pitch again this season.

Garza was diagnosed Monday with a stress reaction in the back of his right elbow, and will be sidelined indefinitely. Brooks Raley will be promoted from Triple-A Iowa to make his Major League debut on Tuesday against the Padres.

Garza has not pitched since July 21 when he had to come out of the game after three innings because of cramping in his right triceps. He had a good bullpen session on Saturday in Los Angeles, but his arm was stiff on Sunday and he was sent back to Chicago to be examined. Tests on Monday revealed the injury.

Cubs reliever Blake Parker was diagnosed with the same injury earlier this year, and he last pitched June 1. He was scheduled to make his first rehab start on Monday for Triple-A Iowa.

Cubs general manager Jed Hoyer would not predict whether there's time for Garza (5-7, 3.91 ERA) to return this year.

"We'll keep reevaluating him and will make that decision when he picks up a ball and starts throwing again," Hoyer said. "To speculate right now on his status for the season wouldn't be right. Today, we got the diagnosis, talked about it and we'll make a decision when it's right. It's too early to speculate on the remainder of the season or when he'll start throwing."

Garza won't be allowed to pick up a baseball for the next two weeks.

"He felt really good, as he told [the media] on Saturday, and that's the surprise of it," Hoyer said. "Matt's a competitor and he'll want to get out there and get going. He'll be eager to get back and we'll wind up holding him back to an extent."

With the loss of Garza, Jeff Samardzija now has senior status on the Cubs rotation, and this is his first year as a full-time starter.

"It's the way things go sometimes," Samardzija said. "You just have to be ready for anything."

Samardzija expected Garza to return sooner rather than later.

"Garza really loves to pitch," Samardzija said. "He's not a guy to take a day or ask for a day or complain about how he feels. You know if he's not feeling well, he's definitely not feeling well. Hopefully, he can get back as soon as possible. When you have a guy like Garza, it turns the rotation up a notch for sure."

Raley's debut set as Garza hits shelf

SAN DIEGO -- Left-hander Brooks Raley will make his Major League debut Tuesday, replacing Matt Garza in the Cubs rotation.

Garza is sidelined indefinitely with a stress reaction in his right elbow, diagnosed on Monday.

Raley, 24, will be the 14th rookie the Cubs have used this season, and seventh pitcher. He was the Cubs' Pitcher of the Month for July after posting a 2.12 ERA (seven earned runs over 29 2/3 innings). He walked 12 and struck out 28, holding opponents to a .254 average. His 2.12 ERA was the fourth-lowest in the Pacific Coast League. He gave up two or fewer runs in each of his five outings while posting three quality starts.

"He's a guy who can pitch in and out, [throws a] cutter, two-seamer, four-seamer, nothing overpowering," Cubs manager Dale Sveum said. "He's not going to probably strike a lot of guys out. He's going to pitch to contact. His command is pretty good, his mound presence is outstanding. His breaking ball [is good], he has a plus changeup. He's a lot like Travis Wood with a breaking ball a work in progress."

A sixth-round pick in 2009, Raley began the season with Double-A Tennessee and was 2-2 with a 3.51 ERA in eight starts, striking out 29 over 48 2/3 innings. He was bumped up to Triple-A Iowa, where he was 4-8 with a 3.62 ERA in 14 starts. He struck out 69 and walked 28 over 82 innings, and opponents were batting .272 against him. In his last start, Thursday, he gave up six runs on 10 hits over six innings.

A roster move will be made on Tuesday, with Garza heading to the disabled list.

Rizzo returns to San Diego

SAN DIEGO -- Anthony Rizzo gave his Cubs teammates a first-hand scouting report Monday on Petco Park. He should know. It was his home park last season, his first in the big leagues.

Monday was Rizzo's first game back in San Diego after he was traded in the offseason from the Padres to the Cubs. He called last year a learning experience, and said he made the adjustments he needed to do. He had to. Rizzo batted .141 in 49 games with San Diego, including .171 at Petco.

"The first time around here was crazy, and it was a lot to take in and a lot of different things happened and it obviously didn't go the way I wanted," Rizzo said. "I was prepared more this time when I came up [to the Cubs]. I was more anxious to get on the field again to prove myself."

He's done that, winning National League Rookie of the Month in July after batting .330 with seven home runs and 17 RBIs in 25 games. Petco is not very hitter friendly. Was that the problem?

"The ballpark could've been a T-ball field and I couldn't hit the ball," Rizzo said. "I just wasn't hitting the ball. That's the biggest thing. I wasn't hitting the fastball or pretty much anything. I made some adjustments, and I'm happy where I'm at, and I want to continue to keep getting better."

OK, so what was the problem?

"Probably between my ears," he said. "It's just one of those things. I had to start hitting better, and made the adjustment. ... You try to get five hits in one at-bat is nearly impossible -- I think."

This series also is a return trip for Cubs general manager Jed Hoyer, who had the same job with the Padres for two seasons before joining Theo Epstein's staff in Chicago.

"I'm sure I'll enjoy myself and bounce around and see a lot of people," Hoyer said about coming back. "It's fun to be back in San Diego to see friends. I love this ballpark. It's a great place to watch a game. It's obviously a beautiful city. You always have mixed feelings when you go back to a place you enjoy, and I do have mixed feelings, but it's fun to come back here with the Cubs and hopefully we can win the series."

LaHair's playing time will be hard to come by

SAN DIEGO -- Bryan LaHair is the odd man out for the second time this season. LaHair lost the first-base job to Anthony Rizzo on June 26, and now has been bumped from the Cubs outfield with the arrival of Brett Jackson.

"It's going to be tough getting playing time," manager Dale Sveum said of LaHair, who was one of the Cubs' two All-Stars. "Unfortunately, these things happened to him twice with our two biggest prospects coming up in the same season and him getting bumped from a position."

LaHair batted .194 in 21 July games, and was 3-for-9 in four games in August.

Extra bases

• Jackson batted leadoff Monday in his second big league game, which he did for 56 games at Triple-A Iowa. Jackson batted .279 against left-handers at Iowa, and got a hit off Dodgers southpaw Randy Choate on Sunday.

• The Cubs don't have much depth pitching-wise at Iowa. Rodrigo Lopez, who started for the Cubs last year, is on the disabled list with a strained right shoulder.

"God forbid something happened because you'd have to ad-lib it," Sveum said. "You can't ad-lib too much because you never know when an injury might happen."

One option is Casey Coleman, who had a solid outing on Sunday, striking out eight over six shutout innings in a 2-1 loss to Reno.

• Double-A Tennessee's Justin Bour was named the Southern League Hitter of the Week for July 30-Aug. 5. He batted .409 (9-for-22) with three home runs and nine RBIs.

• Lendy Castillo, the Cubs' pick in the Rule 5 Draft, will begin a rehab assignment Monday with Tennessee. Castillo, 22, appeared in seven games with the Cubs before he was sidelined with a groin injury.