Source: Minnesota Vikings WR Justin Jefferson has shoulder sprain

EAGAN, Minn. -- Vikings wide receiver Justin Jefferson sprained the AC joint in his left shoulder, a source told ESPN's Adam Schefter, but the injury is not considered serious.

The injury happened at the halfway point of Minnesota's Friday afternoon practice. Jefferson fell onto his left shoulder after he caught a slant from quarterback Kirk Cousins with cornerback Bashaud Breeland in coverage in 11-on-11 drills and immediately grabbed the shoulder. It was the third straight target for Jefferson, who caught a 22-yard pass on a corner route two plays earlier.

Jefferson stayed on the ground momentarily while trainers tended to him before he walked off the field under his own power while holding his left arm in place.

A source told ESPN that Jefferson will undergo further testing this weekend.

Jefferson totaled 1,400 receiving yards last season, the most by any rookie in the Super Bowl era (since 1966).