PHOENIX -- Padres second baseman David Eckstein was placed on the 15-day disabled list Monday as San Diego made a series of roster moves.

Eckstein sustained what Padres manager Bud Black said was a first-degree strain of his right hamstring trying to leg out a ground ball during the bottom of the 12th inning in Sunday's 7-6 loss to the Dodgers at PETCO Park. A first-degree strain is the mildest form of the injury.

Even so, Black said the team's trainers couldn't determine at this point how long Eckstein will be out.

"I think we'll get a pretty good determination where this thing is going in four or five days," Black said before Monday night's game against the D-backs at Chase Field. "Whether the recovery is happening fast or whether it will take a little longer."

Eckstein, who traveled with the team, said he was hoping for a swift return.

"It's not a tear," Eckstein said. "And it definitely didn't get worse overnight. So that's definitely a good sign. I probably wouldn't notice if I was walking, but if I tried to push it, I'd feel it grab. So we're hoping this is a short thing. I'm on the 15-day DL. Coming back in 15 days, hopefully that won't be a problem."

When he returns, Eckstein will be wearing a different number -- 22 -- which is his wife's favorite number and the number he wore with the Angels and the Cardinals. Eckstein has worn No. 3 since he joined the Padres during Spring Training. No. 22 had been reserved for pitcher Mark Prior, but it became available when Prior missed the season because of arm problems.

"It's a long story," Eckstein said. "I had never picked my number. I was given 22. But my wife's birthday is on Sept. 22. We had our first date on Sept. 22, when she turned 22. And our whole wedding was 22-themed because of it."

The Padres also activated pitcher Luke Gregerson from the 15-day DL and recalled pitcher Mike Eckstrom from Triple-A Portland. Ryan Webb, another pitcher acquired Sunday from Oakland in a trade that sent outfielder Scott Hairston to the A's, joined the club while left-hander Joe Thatcher was dispatched to Portland.

The moves gave the Padres 14 pitchers and 11 position players for the moment, although another move that includes a position player coming from Portland will undoubtedly be made Tuesday, Black said. For Monday night's game, Black had only infielder Edgar Gonzalez, outfielder Kyle Blanks and catcher Jose Lobaton on the bench.

Gregerson had been on the DL since June 16 (retroactive to June 8) with a strained right shoulder.

The injury to Eckstein continued a bad run for the Padres, who have lost their two top pitchers (Jake Peavy and Chris Young), their two catchers (Nick Hundley and Henry Blanco), their starting veteran right fielder (Brian Giles) and now their starting second baseman to injury this season, among others.

"It's been tough," Black said. "This is the worst run [of injuries] I've ever seen. Maybe it's happened during some short window of time sometime during my career, but certainly not in the three years I've been here as manager."