[Yahoo Sports] Quarterback Matt Cassel could miss two to four weeks with a strained medial collateral ligament in his right knee, a source within the Kansas City Chiefs organization said.

Cassel, who the Chiefs acquired in a trade with New England this offseason, was hurt Saturday night in an exhibition game against Seattle. The injury is not expected to require surgery because MCL injuries usually heal on their own.

However, the injury means Cassel could miss the Chiefs’ season opener at Baltimore on Sept. 13.

Cassel also suffered an ankle injury, but that was not considered as serious as the MCL injury.