49ers 1st round pick Mykel Williams injures knee in practice

There were a lot of positives to take away from the San Francisco 49ers joint practice with the Denver Broncos on Thursday.

But all of that may get overshadowed by a key injury.

Midway through the team session, 49ers first-round pick Mykel Williams went down with a left knee injury and gingerly left the field.

After practice head coach Kyle Shanahan addressed reporters about the injury.

“Hopefully, just hyperextended his knee," he said. "We’ll get a further examination now, but it looked good when we examined him." 

Williams will have further testing on the knee in the coming days.

It's a potential injury the 49ers can't afford.

After struggling to stop the run last season, San Francisco attempted to address the issue with key selections in the draft - Williams, second-round pick Alfred Collins (Texas) and fourth-round pick C.J. West (Indiana).

Early in camp, it appeared as though both Williams and West were on track to become starters Week 1, with Williams drawing particular praise as a player who could become a star as he develops.

The edge-rusher spot opposite All-Pro Nick Bosa has been a revolving door in recent seasons - with no single player capitalizing on the frequent double-team of Bosa.

Williams was drafted to be the long-term answer at that spot.

Until the test results confirm no structural damage to the knee, the 49ers are likely to have a nervous couple of days.