Arizona Cardinals rookie wide receiver Marvin Harrison Jr. collapsed on the field and left Sunday’s 34-13 loss to the Green Bay Packers early following an inadvertent hit to the head on a pass play.

The play took place in the second quarter at Lambeau Field. Cardinals quarterback Kyler Murray targeted Harrison on a pass over the middle. Packers cornerback Jaire Alexander broke up the pass and knocked Harrison to the turf. As Harrison fell, the crown of his helmet hit linebacker Isaiah McDuffie in the thigh, sending his head snapping backward.

Harrison got up after the hit, clearly dazed. He immediately fell back to the turf.

He went to the sideline medical tent and then left for the locker room with athletic trainers. The Cardinals announced before halftime that he was being evaluated for a concussion and ruled him out before the start of the third quarter.

The injury is a tough blow for Harrison in his sixth NFL game and for a Cardinals team struggling to move the ball. A first-round draft pick, Harrison was Arizona’s leading receiver through Week 5 with 17 catches for 279 yards and four touchdowns. The Cardinals went into halftime against the Packers trailing, 24-10. They scored just a single field goal the rest of the way, and committed a pair of turnovers on back-to-back drives en route to the 21-point loss. That dropped them to 2-4 on the season.