The Angels' Mike Trout, still suffering from back problems, left Tuesday night's game after the first inning.
After missing two games due to back stiffness, the center fielder started the game against the Houston Astros at Minute Maid Park and struck out swinging in the first inning.
Trout then reported "mid-back discomfort," the Angels said, and he was replaced in the second inning by Collin Cowgill.
Trout will be evaluated by a doctor in Houston on Wednesday, Manager Mike Scioscia said. "He'll have some studies done here," Scioscia said. "We'll definitely take a half-step back here and find out exactly what's going on. [Trout] can't think of one thing that he did over the course of the last three or four days that caused it."
Trout, 22, entered the game batting .294 with 11 home runs and 38 runs batted in.
The Angels were looking forward to being back at full strength Tuesday night because slugger Josh Hamilton also returned after nearly two months on the disabled list.