Wells will be evaluated by team doctors Tuesday and the Angels will make a move to replace Wells on the roster before the start of Tuesday's game against Chicago.
"It feels better now than when it first happened, which is a good thing," Wells said. "Tomorrow will be a good sign in telling me what is going on."
After hitting a ground ball to third base, Wells was helped off the field by Angels manager Mike Scioscia and a trainer.
"Vernon is pretty tough and when he didn't run down that line, I knew something was wrong," Torii Hunter said. "It is pretty serious stuff with the groin, I just hope he heals quickly."
While Wells has struggled at the plate with only a .183 batting average, along with four home runs and 13 RBIs, the Angels left fielder had begun to find his stride at the plate, hitting three home runs and seven RBIs in his last seven games. He went 1-for-2 on Monday.
Scioscia said it is a big blow to the middle of his lineup.
"Vernon was starting to come alive and swing the bat much better," Scioscia said. "We definitely talked about the importance of getting him into his game. That is obviously going to be pushed back now. We'll get an evaluation and see how long it is."
While Wells has been swinging the bat better of late, the most frustrating thing for him "is that I won't be out there, good or bad, whatever my numbers are," Wells said. "It is frustrating just to have to sit by and watch."
While the Angels will call up a player from Triple-A Salt Lake on Tuesday, Scioscia said that "we are going to get it done with the guys on the roster right now and get some more at-bats for some guys and less days off for others. We have a little versatility right now with some positions, but our issue with organizational depth, we don't have a lot of guys in Triple-A killing the ball right now."
Asked if he would consider calling up prospect Mike Trout, who is currently playing with the Double-A Arkansas Travelers, Scioscia simply said, "No."
Alexi Amarista, who began the game at second base, replaced Wells in left field at the start of the fifth inning. Howard Kendrick replaced Amarista at second.
Quinn Roberts is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.