Provo » BYU receiver McKay Jacobson has a pulled hamstring and will be out for 4-6 weeks, coach Bronco Mendenhall announced at his Monday morning news conference.
Jacobson, a sophomore, was one of BYU's leading receivers the first four games of the season, catching 11 passes for 280 yards and three touchdowns.
He injured the hamstring during pregame stretching exercises, Mendenhall said, and did not play in Friday's 35-17 win over Utah State.
An MRI performed on Saturday revealed the damage, which Mendenhall said is "way, way up high --- kind of at the origin part of the muscle."
Mendenhall said BYU trainer Kevin Morris said it was "very rare" for that type of injury to happen during stretching, and that the injury is at a different point than the one that sidelined Jacobson for most of spring camp.
Junior receiver Luke Ashworth will be Jacobson's primary replacement. Ashworth caught five passes for 91 yards and a TD against USU.
Freshman Brett Thompson will be the next receiver in at the "Z" position, while special teams player B.J. Peterson could also see more action with the offense.
Jacobson was also BYU's primary punt returner. That position will be filled by O'Neill Chambers, while Chambers and J.J. DiLuigi will be the kickoff return tandem.
Mendenhall said special teams players Steven Thomas and Tucker Lamb suffered concussions on Friday and will be questionable for the UNLV game on Saturday in Las Vegas.
Offensive lineman Matt Reynolds also went out of Friday's game briefly, but he said Monday that he had a leg cramp and is now fine.