Marshall suffered the injury during the Bucks' win over the New York Knicks in London on Thursday. The third-year player went down in the second quarter after playing only four minutes in the game. After heading to the locker room, he was able to walk out of the arena after the game with a slight limp.
Marshall underwent an MRI on Saturday that confirmed the injury after being evaluated by team orthopaedic physician Dr. Michael Gordon. Marshall will have surgery at a date to be determined.
In 28 games (three starts) this season, Marshall was averaging 4.2 points, 3.1 assists and 1.0 rebounds in 14.9 minutes.
The Bucks claimed Marshall off waivers in July from the Los Angeles Lakers. Marshall played in 54 games with the Lakers, starting 45, and averaged a career-high 8 points, 8.8 assists and 2.9 rebounds in 29 minutes.
Marshall, 23, was selected with the 13th pick in the 2012 draft by the Phoenix Suns. After playing in 48 games with the Suns, he was traded to the Washington Wizards as part of a five-player deal. Marshall was waived by the Wizards three days later and landed with the Delaware 87ers of the NBA D-League.
Behind starting point guard Brandon Knight, the Bucks also have Jerryd Bayless, who signed with Milwaukee in July. Second-year guard Nate Wolters was waived last week to make room for forward Kenyon Martin, who signed a 10-day contract with the team on Friday.
Milwaukee also lost first-round draft pick Jabari Parker to a torn ACL last month, as well as second-round pick Damien Inglis, who underwent ankle surgery earlier this month.
The Bucks (21-19) entered Saturday fifth in the Eastern Conference, 11 games behind the Atlanta Hawks.
Milwaukee will host the Toronto Raptors on Monday.
- Mike Fiammetta