Howard, who was placed on the disabled list Saturday with inflammation in his left knee, was diagnosed with a torn meniscus and will go under the knife, the Phillies said.
The Philadelphia first baseman had been dealing with knee soreness for several weeks before the diagnosis. He was hitting .266 with 11 home runs and 43 RBI over 80 games this season.
To take his spot on the roster, the Phils recalled Darin Ruf from Class AAA Lehigh Valley, where he has hit .266 with seven homers and 46 RBI over 82 games this season.
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