49ers linebacker Dre Greenlaw is set to undergo surgery and could miss a decent amount of time.
On Thursday, 49ers general manager John Lynch provided some details on the injury, including that Greenlaw tweaked it during his pick-six against the Detroit Lions in San Francisco's 41-33 win.
"So, he is going to have surgery," Lynch told KNBR's "Tolbert, Krueger and Brooks." "They got a couple of opinions on the groin. It's a core muscle injury that Dre's been dealing with here for the last couple of weeks, and he did a great job kind of battling through it. [He] had a big impact on the game against Detroit.
"It was actually on the pick-six that he kinda re-tweaked it, and at some point, we scanned it, and this core muscle injury just continued to get worse. It got to the point where we felt the best interest for everyone was to go ahead and handle it now."
Lynch noted that the reported four-to-six-week timeline for Greenlaw's recovery should be accurate.
Greenlaw is the third important 49er to go out with an injury this week. The 49ers lost cornerback Jason Verrett to a torn ACL and running back Raheem Mostert elected to undergo a season-ending procedure on his knee.
The 49ers expect to have Greenlaw back this season, but there's no doubt his absence will leave a big hole to fill on the defensive side of the ball.
"It's a loss, to say the least," Lynch said. "The good news is that all indications are we'll have him back later this season. We look forward to that. We'll have to hold the fort down until then."