The 49ers have been struck by the injury bug early on in 2020, and one of the biggest losses comes on their vaunted defense.
Defensive end Nick Bosa went down in the first quarter of Week 2 against the New York Jets with a left knee injury. It was announced the next day that Bosa suffered a torn anterior cruciate ligament (ACL) in that left knee and that he'll miss the remainder of the season.
Bosa was the NFL's Defensive Rookie of the Year in 2019. He recorded nine sacks and was a key component of the high-end defense that led the 49ers to the Super Bowl. If San Francisco wants to make it back to that stage in 2020, it'll have to do so without Bosa.
Here's what you need to know about Bosa's injury and when he might return for the 49ers:
How long will Nick Bosa be out?
Bosa was placed on Injured Reserve on Sept. 23, and the 49ers have already announced that he won't be returning during the 2020 season. His fellow defensive lineman Solomon Thomas tore his ACL in the same game.
"We will be back stronger than ever with a vengeance," Thomas tweeted. "I promise."
Torn ACLs clasically take about a year for a full recovery. That means that Bosa will likely be a question mark for the opening of the 2021 season, at least until San Francisco's training camp opens up next summer and people can get a look at how recovered Bosa is.
Bosa was scheduled to undergo surgery during the week of Sept. 26, according to Adam Schefter. Schefter reported that Bosa's knee also showed additional cartilage damage that the 49ers hope won't hinder his recovery.
What is Nick Bosa's injury?
Bosa suffered a tear of the anterior cruciate ligament in his left knee. The ACL is the ligament that connects the thighbone to the shinbone at the knee. It helps prevent the top and bottom of the knee from sliding back and forth.
In Bosa's case, he tore the ACL while being blocked down field. As Bosa fell to the ground, his left leg got caught underneath the rest of his body and bent at an unnatural angle.
ACL reconstruction surgery normally takes a tendon from another part of the knee and puts it where the original ligament was, according to the Mayo Clinic.
Nick Bosa injury timeline
Dec. 1 - More social media video suggests Bosa is very strong.
Nov. 4 - A video of Bosa doing his physical therapy is posted on social media.
Sept. 26 - Bosa was scheduled to have his ACL surgery during the week of the 26th, according to ESPN.
Sept. 23 - Bosa was procedurally placed on Injured Reserve.
Sept. 21 - The 49ers announce that Bosa has torn his ACL and will miss the remainder of the season.
Sept. 20 - Bosa leaves the 49ers' Week 2 game at the Jets in the first quarter on a cart.
Nick Bosa injury updates
Nov. 4 - Bosa is undergoing physical therapy at MOTUS Specialists in Orange County, who have also treated Russell Wilson in the past.
Sept. 21 - The 49ers officially announce that Bosa's ACL is torn.
Sept. 20 - Kyle Shanahan said that he feared Bosa had torn his ACL, according to Ian Rapoport.