San Francisco 49ers defensive tackle Alfred Collins will miss the entire season after tearing his patellar tendon, coach Kyle Shanahan announced Wednesday. The injury occurred during practice at AAMI Park on Tuesday, just days before the team's season opener against the Los Angeles Rams.

Collins was expected to be a significant contributor as the probable starting nose tackle for the 49ers this season. His absence places additional strain on a defensive line already facing depth challenges. Several other defensive linemen are also dealing with injuries: defensive tackle Gracen Halton and defensive end Romello Height are limited with ankle injuries, while undrafted rookie defensive tackle James Thompson Jr. missed practice with a hamstring issue.

"That was a big loss," Shanahan said. "We've lost two D-linemen pretty much for the year after (final roster) cuts, before the first game, which is going to be a huge challenge. I'm hurting for Alfred. It's real unfortunate for him."

Last season, Collins recorded 17 tackles in 16 games as a backup. He is also remembered for a pivotal play in the 49ers' overtime victory against the Rams last season, where he forced and recovered a fumble near the goal line.

Despite the setback for Collins, tight end George Kittle and defensive end Nick Bosa are on track to play in Friday morning's game in Melbourne, Australia, though Shanahan indicated their playing time might be managed. Bosa, who experienced a shortened season last year due to a knee injury, has expressed confidence in his own readiness and offered support to Collins.

"He just has to know that there's a light at the end of the tunnel," Bosa said of Collins. "I told him I've been through it a few times, so he just needs to take it one day at a time."