The Timbers winger underwent surgery after suffering the injury to his left knee in training on Monday.
Zizzo suffered the injury in training on Monday, a day after he appeared as a second-half substitute in the Timbers' 3-3 draw with the New York Red Bulls. It is not the first damage Zizzo has had to his left knee, as he has twice suffered a left ACL tear, once in 2009 and again in 2011.
The 25-year-old Zizzo is in his third season with Portland after the club acquired him in a trade with Chivas USA prior to its expansion season. In 51 matches as a Timber, Zizzo, who is a former U.S. youth national team standout and has one senior cap to his name, has a goal and seven assists.