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9/1/2014 7:45 P.M. ET

Alvarez day to day with left oblique strain

MIAMI -- The Marlins' rotation has taken plenty of hits this season. Just when it seemed like the club was past all the injuries, Henderson Alvarez left Monday's 9-6 win over the Mets in the third inning with a left oblique strain.

Whether Alvarez will be able to return from the injury has not been determined, but the 24-year-old was listed as day to day.

"Those obliques are dicey, for sure," manager Mike Redmond said. "We'll see. That's something we'll evaluate over the next couple days, as far as his availability for his next start."

Alvarez was seen sporting a wrap around his left side before the game, but he breezed through his first two innings. He retired all six batters and needed just 23 pitches to do it.

But after giving up a leadoff homer to Mets rookie Dilson Herrera in the third -- the fifth one he's allowed since returning from a stint on the disabled list with right shoulder inflammation -- Alvarez's day spiraled toward its end.

The next four batters reached base, although Alvarez did get a forceout on Juan Lagares' tapper to short. With the bases loaded, Alvarez was unable to retire David Wright -- who hit a two-run single to center fielder Marcell Ozuna. Another run came in when Ozuna airmailed his throw to third into the Marlins' dugout, which also allowed Wright to reach second.

Redmond and trainer Mike Kozak were quick to come out and check on Alvarez, but he circled the bump as if he was trying to avoid being removed from the game.

Redmond elected to have Brad Hand relieve him anyway. Alvarez threw 40 pitches and was charged with three earned runs on three hits and a walk in 2 1/3 innings.

Pain has nagged Alvarez since his last start against the Angels on Wednesday, when he allowed five earned runs over 6 1/3 innings and felt a tweak in his side.

"I didn't want to miss another outing," Alvarez said. "I wanted to keep pitching the way I know I can. ... I wasn't 100 percent, but I went out to battle."

The injury couldn't happen at a worse time, as the Marlins moved 5 1/2 games back in the Wild Card race after their win and the Brewers' loss to the Cubs. The right-hander has anchored the rotation during an All-Star season in which he's posted a 2.88 ERA, a 10-6 record and 14 quality outings in 26 starts.

Additionally, the Marlins have won 18 of his starts. Alvarez has been their ace in the absence of Jose Fernandez, and losing him for the rest of the season could be costly.

"As much as we need him to pitch, we're not going to let him go out there and jeopardize himself," Redmond said. "Today, he couldn't get it going. So it's going to have to get a lot better for him to pitch."

Jennings, Capps return for Marlins' stretch run

MIAMI -- Injuries early in the season forced the Marlins to change the look of their bullpen on more than one occasion. But as rosters expanded on Monday, Miami was finally able to bring in some reinforcements, as it reinstated Carter Capps (right elbow) and Dan Jennings (concussion) from the 60-day and 15-day disabled lists, respectively.

Jennings hasn't seen action in the Majors since being struck on the head by a line drive off the bat of Jordy Mercer in the seventh inning at Pittsburgh on Aug. 7.

He was placed on the 7-day concussion list the following day, but was playing catch at Marlins Park a week later. At the time, Jennings was still feeling some tenderness on the left side of his head but was confident he'd be completely symptom-free by the time rosters could expand.

"Obviously, my first thought was, 'Year's over,'" Jennings said. "Now, I'm back and able to play again. It's awesome."

The rehab process seemed lengthy for the 27-year-old, who had never been on the disabled list. Jennings progressed quickly, though. Three days after his first outing with the Gulf Coast League Marlins on Aug. 19, he was transferred to the 15-day disabled list and moved over to Class A Advanced Jupiter to continue his rehab.

In four total appearances, Jennings threw seven scoreless innings and gave up three hits and a walk, while striking out nine batters. Pitching in "less tense situations," he said, afforded him the chance to get over the fear of comebackers.

He did have a close call with a ground ball hit to his feet, but it didn't bother him.

"When something like that happens, the team, as well as myself, want to make sure I can get back on the mound and still pitch," Jennings said. "I'm fortunate that I didn't have any lapses or anything like that, that I was able to just get back on [the mound] and pitch -- and it felt natural."

His only lingering fear is the possibility of allowing a pitch to cross the middle of the plate, making the ball hittable like it did in the sequence against Mercer.

"[It's] just fear that it's a bad pitch and they're gonna hit it in general, and that's obviously something you try to avoid," Jennings said.

Meanwhile, Capps has been sidelined with right elbow inflammation since the end of May. He was shut down for two months before he started playing catch in August. His first rehab appearance didn't come until Aug. 25.

The hard-throwing righty pitched 3 1/3 scoreless innings for the GCL Marlins and the Hammerheads. He threw two of those frames in his latest outing on Saturday, during which he recorded two strikeouts.

"It definitely felt like a long time coming, but the training staff just assured me that they thought I could be back around September," Capps said. "Luckily, I didn't have any setbacks. I was pretty grateful for that and just really blessed that I didn't have any more problems than I did. Caught it early. Definitely glad to be back."

Although the path back to the Majors has been a long one, Capps feels more mechanically sound than he felt even during Spring Training. In the months leading up to the initial diagnosis, he was experiencing issues on extension -- especially when throwing his fastball, which, according to FanGraphs, averaged 97.7 miles per hour this year.

The issues became readily apparent in his final outings on May 21 and May 25, when he yielded three earned runs on four hits (one a homer) across two innings. In seven games before that, he'd posted a 0.90 ERA and struck out 14 batters -- something he hopes to get back to as the Marlins push for the playoffs.

"I really wanted to go into the offseason not leaving a bad taste in the Marlins' mouth," Capps said. "They obviously gave me a great opportunity to be up here, and I definitely want to prove that I can pitch up here and pitch healthy."

Maria Torres is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.