Oakland Athletics closer Grant Balfour will miss 4-6 weeks with a knee injury.
Balfour was bothered by knee soreness at the end of the 2012 season. He was hurting again Wednesday during batting practice and tests revealed a torn meniscus in his right knee that required surgery Thursday.
"I knew with the way I was feeling I wouldn't have been able to pitch through it all season," Balfour said.
Balfour could still be ready for the start of the regular season, which Balfour indicated was the reason for having surgery.