Alvarez exited the Marlins' 9-6 win over the Mets on Monday in the third inning with a left oblique strain. On either Wednesday or Thursday, he is expected to throw a bullpen session to determine if he is ready for his next start.
"That's to be determined, and it's really depending on how he feels. The plan is for him to throw a bullpen to show if he is ready to go," manager Mike Redmond said. "We definitely want to make sure he's feeling good, and is 100 percent ready to go."
If Alvarez is not, an option to fill in is Miami's No. 1 prospect, Andrew Heaney.
Heaney, right-hander Anthony DeSclafani, infielder Enrique Hernandez and first baseman Justin Bour were recalled from Triple-A New Orleans on Tuesday as rosters expanded for September.
DeSclafani adds long-relief/spot depth, and Hernandez and Bour become bench players for the stretch run.
Exactly how Heaney will be used has yet to be determined. The 23-year-old made four starts for Miami in the first half, going 0-3 with a 6.53 ERA. His last start was on July 5 at St. Louis, where he gave up five runs in 3 2/3 innings.
Heaney had a solid season in the Minor Leagues, posting a 9-6 record with a 3.28 ERA in 137 1/3 innings between Double-A Jacksonville and Triple-A New Orleans.
With the Marlins, Heaney will get a chance to refine his skills with pitching coach Chuck Hernandez.
"The plan is for him to continue to pitch, and to work," Redmond said. "I know he will work with Chuck on a lot of different things. We'll plan on where we can slot him into some games, and get him some work."
The Marlins are off on Thursday, which adds some flexibility on when Alvarez returns.
"I woke up feeling better," Alvarez said. "I'm just going to undergo treatment and we'll see how it goes from there. I've never had an oblique problem before."