The 37-year-old left Wednesday's game against the Chicago White Sox in the seventh, one inning after he was thrown out trying to stretch a single into a double.
Angels manager Mike Scioscia said Pujols had an MRI, which showed tendinitis in the hamstring.
"Nothing more than that," Scioscia said. "It's sore."
Los Angeles is on a 10-game trip that includes a pair of three-game series at National League ballparks, where there is no designated hitter.
"We're just going to take a little precaution to make sure he's a certain level before he plays first base," Scioscia said. "We're just going to read it on a daily basis."
Pujols is hitting .247 with five homers and 32 RBIs, usually hitting third in the order behind AL MVP Mike Trout.
"There's obviously going to be a little hole in your lineup, and you just work around it," Scioscia said.
After the game, Scioscia said Pujols had not been available as a pinch hitter.