LONDON -- Dallas Cowboys cornerback Tyler Patmon suffered a sprained medial collateral ligament in his left knee and could miss three-to-four weeks, according to a source.

Patmon is set for more exams after the team arrives in Dallas. He was hurt in the first half of Sunday's 31-17 win against the Jacksonville Jaguars.

The Cowboys will likely have to add a cornerback in his absence because they have only three on the active roster in Brandon Carr, Orlando Scandrick and Sterling Moore.

The Cowboys have Micah Pellerin on the practice squad.

Dallas started using more dime defenses in the past two games in part because of Patmon's development and injuries at linebacker. Patmon had an interception return for a touchdown against the Arizona Cardinals.

After Patmon was injured, the Cowboys predominantly went with their nickel defense against the Jaguars but used safety Jeff Heath as the sixth defensive back occasionally.

Depending on how Patmon recovers he could miss two-to-three games with the Cowboys having their bye week this week.