The San Francisco 49ers are 3-0, but they continue to suffer from awful injury luck.

A day on from a dramatic 16-15 win over the Arizona Cardinals, the 49ers were hit by a major injury setback with the news that defensive end Nick Bosa, who left the game in the first half with a knee issue, had sustained a season-ending torn ACL.

The 49ers were hopeful Bosa had avoided any damage to ACL following initial checks on the sideline in their home opener at Levi’s Stadium. However, MRI scans on Monday revealed a clean tear that will require surgery, according to a report from ESPN’s Adam Schefter.

It marks the second time in Bosa’s career that he has suffered a torn ACL, having also done so in Week 2 of the 2020 season.

His loss represents a huge blow to a defensive line that has produced vastly improved play through three weeks after uncharacteristic struggles up front last season.

The return of Robert Saleh for a second spell in charge as defensive coordinator has had a hugely positive impact, with rookie first-round pick Mykel Williams among those to impress. Bryce Huff, acquired for a conditional fifth-round pick in a trade with the Philadelphia Eagles in June, has two sacks to his name already.

Much of San Francisco’s hopes on defense were tied to having the chance to get Bosa and Huff on the field at the same time. Now, with the 49ers robbed of one half of a duo that looked potentially devastating through two games, Huff will have to take on more of the burden.

Bosa, the 2022 Defensive Player of the Year, sees his season end after recording two sacks and four tackles for loss while forcing two fumbles, including one that clinched San Francisco’s Week 1 win over the Seattle Seahawks.

The long-term saving grace for the 49ers is that Bosa bounced back from his 2020 injury by posting double-digit sacks in each of the next three seasons, including 18.5 in his Defensive Player of the Year campaign. Still, that is likely to be cold comfort for now as the Niners move forward towards their Week 4 clash with the Jacksonville Jaguars without one of the game’s premier defenders.