Portland, OR (Sports Network) - The Portland Timbers announced Tuesday that midfielder Sal Zizzo has undergone a successful operation to repair a medial meniscus tear in his left knee.

Zizzo concluded Portland's tilt with Red Bull New York on Sunday as a substitute but sustained the injury one day later in training.

The 25-year-old is expected to be out for four weeks.

03/05 12:42:12 ET