"Corey will be re-evaluated tomorrow," manager Lloyd McClendon said after the game. "It didn't look good. We'll know more tomorrow after the MRI. From that, we'll decide what we're going to do."
Nick Franklin was pulled out of Triple-A Tacoma's lineup prior to their game in Sacramento on Sunday and could be rejoining the Mariners in Texas in time for Tuesday's game. If the 23-year-old is added to the roster, he conceivably could take Hart's place on the 25-man roster if Hart needs to go on the 15-day disabled list.
If the Mariners need a temporary DH replacement and right-handed bat to replace Hart, another possibility is Tacoma first baseman Jesus Montero, who is batting .262 with seven home runs and 29 RBIs in 36 games.
Hart started to pull up as he neared the bag and slid awkwardly on the uncontested steal, then stood up and immediately signaled for the trainer. He left the field and was replaced by rookie Stefen Romero.
"Right when I got ready to slide, I felt it," Hart said. "My momentum carried me there, but I kind of knew my game was over. I've never had leg cramps or pulled a leg muscle, so I'm not really sure what it is. But I'll get it checked out just to make sure.
"Hopefully it's just a little strain and isn't anything too big. Other than knees, I've never had leg problems. It can't be worse than I've had before. I don't want anything long term, so hopefully it's just a nuisance."
Hart, 32, missed all of last season with the Brewers after undergoing microfracture surgeries on both knees. He signed a one-year, $6 million contract in free agency with Seattle, with up to another potential $4.65 million in bonuses based on his number of plate appearances.
The two-time National League All-Star is hitting .209 with five home runs and 17 RBIs in 37 games. He was 0-for-1 with a walk before coming out of Sunday's game.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.