"I don't expect him to miss very much time with this," Khalfayan said. "It's a similar injury to J.J. Putz."
Putz, the Mariners' closer, missed about three weeks of Spring Training with a similar strain.
Khalfayan said it's "a more repetitive injury," not caused by any one pitch. He added that "this isn't something necessarily that's going to be a continuing problem for him. It's a very common pitcher's injury. It's a minor injury and Felix's injury is minor.
"We'll just take it on a day-by-day basis and go on how he feels. I would say 10 to 20 days is a reasonable time estimate. I'm a doctor so I know what I'm talking about."