SAN DIEGO -- The Astros have come to grips with losing shortstop Jed Lowrie for four to six weeks with an injury to a nerve in his right leg, but they are still unsure how long starting catcher Jason Castro will be sidelined.

Castro, who was placed on the disabled list on Sunday with what the team is calling right knee effusion, had the knee drained and endured a pain-killing injection on Wednesday in Houston. He hopes to be able to come off the DL next week.

"A pretty significant amount of fluid came out, and it looked like they made a pretty successful draining of it," Castro said. "I had a shot in there, and hopefully, in the next few days, it starts to really feel better and I'm able to get back to being a lot more active and get more aggressive movements and see how it feels from there."

Castro, who missed all of last season after undergoing surgery on the ACL in his right knee, was hitting .254 with two homers and 20 RBIs in 20 games.

As of now the Astros aren't considering another surgery to help repair the knee, Castro said.

"The reason why we took the route we did of draining and giving the shot is so I can try to play the rest of the year and push that back and avoid having to miss any more time," Castro said. "If that's something that comes up later, we'll deal with it then."

Barnett says struggling batters are 'pressing'

SAN DIEGO -- The Astros' recent offensive struggles -- they've hit .194 as a team in the past 17 games entering Wednesday -- are partially a result of the young lineup trying to do too much at the plate, hitting coach Mike Barnett said.

Houston had scored only nine runs in its first five games following the All-Star break, having scored two runs in four consecutive games entering play on Wednesday.

"One thing we're going to talk about is the fact our plan at the plate has not been good," Barnett said. "I look at the swings out of the zone, and it's not good at all, and that just tells me the guys are pressing and don't have a consistent plan. When a specific situation presents itself, we've been pretty good."

The Astros are hitting a Major League-worst .153 with the bases loaded, but in the month of July, they have sent home 14 of the 21 runners they've had at third base and fewer than two outs.

"That tells me [when] the situation is in front of them, they know what they need to do ,and they fall into a plan and are executing," Barnett said. "But we can't have games where 60 percent of our swings are chasing balls out of the zone. It's tough enough to hit at this level as it is, let alone chasing that many pitches night in and night out."

Worth noting

• The Astros signed their seventh-round pick, University of Florida outfielder Preston Tucker, to a contract on Wednesday and assigned him to short-season Tri-City. He was in the lineup for the ValleyCats on Wednesday as designated hitter, batting eighth.