The Jets' front office is breathing a sigh of relief.

An MRI on Sunday revealed that rookie defensive end Leonard Williams suffered a muscle strain behind his right knee, according to a source.

Williams, who was forced to leave Saturday night's game against the Giants in the second quarter, did not suffer any ligament damage. The injury is not expected to be long-term.

That's good news for the Jets, who already will be without defensive tackle Sheldon Richardson for the first four games of the regular season because of a substance-abuse suspension. There's also a very good chance the NFL will hand down another suspension after Richardson's July arrest in Missouri.

Williams, the sixth overall pick in this year's draft, limped off the field in the second quarter of the Jets' 28-18 win at MetLife Stadium. Williams walked off under his own power but was escorted to the locker room by a member of the Jets' medical staff. The initial announcement in the press box was that the former USC pass rusher was questionable to return to the game, and he never made it back onto the field.

A league source said late Saturday night that it was possible that Williams suffered a bone bruise but that a proper diagnosis would not be known until the rookie had an MRI.

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It's unclear how much time Williams could miss because of the injury.

The Jets' third preseason game against the Giants most likely was the final dress rehearsal for starters before the regular season begins Sept. 13.

Thursday's preseason finale against the Eagles will feature second- and third-string players vying for roster spots.