An MRI on Monday revealed a torn meniscus in Ryan Howard's left knee. The surgery and recovery means the slugger will miss 6-8 weeks.
Howard was placed on the disabled list over the weekend, a move which prompted the recall of Darin Ruf from Lehigh Valley.
The Big Piece was hitting .266 with 11 home runs and 43 RBIs this season.
It's the second time in less than two years that Howard will require surgery on his left knee.
Phillies general manager Ruben Amaro Jr. compared Howard's injury to that of Erik Kratz's, who began a rehab assignment with triple-A Lehigh Valley on Monday. Kratz underwent surgery June 12 and could return by this weekend. He is well ahead of schedule.