Phillies manager Charlie Manuel said Ruiz could be back in the starting lineup Wednesday.
The Phillies called up Erik Kratz from Triple-A Lehigh Valley to take Roy Halladay's spot on the 25-man roster Tuesday. They recalled Kratz because the Phillies do not need a fifth starter until early next week against the Dodgers at Citizens Bank Park, and it allows the club to have an extra catcher on the bench while Ruiz is recovering.
Ruiz had an ultrasound on his hamstring Tuesday.
"We just wanted to make sure it wasn't anything more serious than that," Phillies assistant general manager Scott Proefrock said. "I don't think it's anything [serious]. It's not a DL situation."