The Brewers said they will recall pitcher Mike McClendon from Triple-A Nashville on Friday to take his roster spot.
Estrada hit a two-run double in the bottom of the first inning of Wednesday's 8-5 win against the Giants. He began limping as he rounded first base and grabbed at his leg upon reaching second.
"I almost wish I would have struck out on that," Estrada said after the game.
Trainers initially told him he had injured his right hip flexor. Estrada said he felt a "pop" in his quad.
The Brewers inserted Estrada into their rotation on April 21 after a torn left rotator cuff ended Chris Narveson's season. Estrada is 0-3 with a 4.50 ERA in 11 appearances, including six starts.