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9/10/2013 3:27 A.M. ET

Castro out second straight game with sore knee

SEATTLE -- Jason Castro's sore right knee kept the All-Star catcher out of the Astros' lineup for the second game in a row Monday against the Mariners.

Castro aggravated a cyst in his right knee a week ago when he fouled a ball off his leg, and he didn't play until starting back-to-back games at designated hitter on Friday and Saturday in Oakland. He hasn't caught since injuring the knee last Monday in Houston.

"We're at the point right now where we're trying to let my knee calm down a little bit so we're just trying to give it as much rest as possible before we start getting back out," Castro said. "I think going back into kind of playing and running around and stuff, I didn't have the full opportunity to get back to where it was 100 percent and not agitated at all. I think that's where we're at right now, just trying to get it back to being calmed down and built up to get back into catching."

Castro, who missed the entire 2011 season after he underwent surgery to repair the anterior cruciate ligament in his right knee, will likely have to do some squatting, such as catching in the bullpen, before getting behind the plate in a game.

"I'm not really sure when that could be," he said.

When asked if there was a chance he might not catch again this season, Castro didn't seem to think that was a realistic scenario.

"It's day to day, so it just depends on how it starts feeling," he said.

Manager Bo Porter said the last thing the Astros want to do is compromise the health of the player that is likely the team's Most Valuable Player this year.

"He will report to the trainers each and every day the degree of soreness and how he's progressed each day and play it by ear," he said.

Corporan returns from three-week DL stint

SEATTLE -- Three weeks after he suffered a concussion when he was struck in the facemask by a foul tip, Astros catcher Carlos Corporan was activated from the disabled list Monday and started in the series opener against the Mariners at Safeco Field.

Corporan, the Astros' primary backup catcher all season, played in three rehab games at Double-A Corpus Christi, catching seven innings Saturday without any problems. He's hitting .245 with seven homers and 17 RBIs in 50 games entering Monday.

"I thought it was going to be seven days and that was it," Corporan said of his timetable to return to the lineup. "It was one week with symptoms, another trying to get ready and the other to do my rehab. I thought that it was not going to be that serious, but after I got hit and started getting my symptoms it was really scary."

The Astros are going to be cautious with Corporan going forward. Manager Bo Porter said the trainers are prepared to visit with him if he takes another foul ball off his mask.

"Lord willing that's not the case and he's able to catch the whole game and be OK," Porter said.

Corporan left Corpus Christi impressed with the talent the Astros have stockpiled at their Double-A affiliate, which was eliminated from the Texas League playoffs on Sunday.

"Those guys play hard," he said. "I'm telling you, those guys know what they're doing and they've got a good group of young guys waiting for the opportunity to come here and perform."

All-Star Jason Castro and Corporan handled the Astros' catching duties until Aug. 19 when a rash of injuries forced the Astros to call up Max Stassi -- who suffered a concussion Aug. 21 -- and Cody Clark and then trade for Matt Pagnozzi. Castro hasn't caught since Sept. 2 because of a cyst in his right knee.

"The rash of injuries we suffered at the catching position, it happens so fast you don't realize how much you miss Corpy, especially once Castro ended up going down as well," Porter said.

Astros monitoring total innings on young arms

SEATTLE -- After hinting before the game that some of the Astros' young starting pitchers could be shut down before the end of the season, manager Bo Porter announced after Monday's 6-4 victory that the team was doing as much with Jarred Cosart.

Cosart, who worked five innings and allowed only an unearned run, two hits and pitched around a career-high six walks, threw a career-high 153 innings combined between his time in Triple-A Oklahoma City and in 10 impressive starts with the Astros.

"Honestly, I don't have much left," Cosart said Monday night. "My body is tired. This is new for me. Missing time last year with the blisters gave me an extra blow, almost a two-week break for my arm. It's kind of like starting over and I missed no time this year, which was a huge plus for me. That was one of my goals this year, to stay healthy this year and be able to come in next year."

The Astros have been restricting the workload of their young starters by using a six-man rotation for the past month.

Jordan Lyles (153 innings) and Brad Peacock (144 2/3 innings) were approaching career-high innings combined between the Minors and Majors. Lefty Brett Oberholtzer (134 2/3) is still more than 30 innings shy of his career high set in the Minors last year, and Dallas Keuchel (141 1/3 innings threw 174 1/3 innings in the Minors in 2010.

"As we move forward, these guys' next starts, we'll make some decisions on some of these guys," Porter said.

Porter added that he was hoping to get Paul Clemens back in the rotation later this week after he missed his start Sunday with a blister.

Grossman's oblique injury keeps him sidelined

SEATTLE -- Starting left fielder Robbie Grossman appears to be at least a few days from returning to the lineup, considering he's not yet able to swing a bat. Grossman injured his oblique swinging the bat last Tuesday and hasn't played since.

"It's getting better," he said. "When I can swing without pain, I can play. I haven't even taken dry hacks swinging off a tee yet."

Grossman hoped to do that in the next couple of days to test the injury he called "nagging."

"It's a situation where we want to take it day by day and see how he's feeling," Astros manager Bo Porter said. "He's not at the point he can swing. You're almost hesitant to pitch-run him or something like that just because he could get on the bases and have to dive back and now you reaggravated the situation. You have a setback this time of year and it's something that could linger into the offseason."

Grossman has hit safely in 29 of 35 games since he was recalled from Triple-A Oklahoma City on July 27, batting .322 with nine doubles, four homers, 18 RBIs, seven walks and four stolen bases in that span. He appeared in 28 games earlier in the season before being sent down.

Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.