Justin Masterson battles sore knee

The Cleveland Indians will skip Justin Masterson's start on Sunday as the ace battles a sore right knee.

Masterson will throw a bullpen session in two days to evaluate the knee.

"We're going to back Justin up a couple of days," manager Terry Francona said, according to cleveland.com. "His right knee has been bothering him and he's been pitching through it, but it's hard for him to generate power."

Zach McAllister will be added to the rotation in Masterson's absence, but it's expected that either T.J. House or Danny Salazar will make Sunday's start against the Mariners.

Masterson is 4-5 this season with a 5.03 ERA.