Rivera hurt his left quad when he accidentally ran into Mark Teixeria while running down the line to beat out a throw by Alex Rodriguez in the fifth. While the throw was off the mark and Rivera was safe, he was noticeably in pain after losing his footing.
"He's a little sore," Angels manager Mike Scioscia said. "He actually got a charlie horse on his right thigh and then hurt his hamstring after he tried to compensate for the pain on the left.
"Juan got racked up a little bit, and that is why we took him out."
Rivera stayed in the game for the next two innings and grounded into a double play in the sixth before Reggie Willits replaced Rivera in left field in the eighth.
Rivera has been on a roll at the plate lately, becoming one of the hottest hitters in the American League. Since June 1, Rivera entered Friday leading the AL with 33 RBIs, ranking second in total bases with 83.
While Scioscia wants to have Rivera's hot bat in the lineup, especially with slugging outfielders Torii Hunter and Vladimir Guerrero on the 15-day disabled list, he knows better than to rush an injury like a hamstring.
"We would like to at least get his bat in there to be the designated hitter, but hamstrings are a different animal -- you don't want to take the chance, especially when you still have to run," Scioscia said. "You want to give it time to calm down.
"If he can and it is just a little stiffness and not any heightened risk, we will take a look at it Saturday."
Quinn Roberts is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.