SANTA CLARA, Calif. — Christian McCaffrey, the standout running back for the San Francisco 49ers, has been ruled out for the remainder of the regular season due to an injury to his right knee, but he will not require surgery.

On Monday, head coach Kyle Shanahan announced that McCaffrey is expected to be sidelined for a minimum of six weeks after sustaining a posterior cruciate ligament injury during Sunday night’s defeat against the Buffalo Bills. This marks the second occasion this season that McCaffrey will be placed on injured reserve, having previously missed the first eight games of the season due to Achilles tendinitis.

The difficulties continue for the 49ers as they lost Jordan Mason, McCaffrey’s backup, to injury; Mason is also facing a stay on injured reserve due to a high ankle sprain sustained in the same match against the Bills.

This season has been particularly challenging for McCaffrey, who was honored as the 2023 AP Offensive Player of the Year prior to receiving a significant contract extension in the offseason. Early in training camp, he suffered an Achilles tendon injury, causing him to miss the initial eight games of the season. Upon returning, McCaffrey rushed for only 149 yards over 43 carries in his first three games as he struggled to regain his peak performance.

However, he showed improvement during the game against Buffalo, amassing seven carries for 53 yards, including a season-long run of 19 yards. His knee injury occurred during an 18-yard run in the second quarter, and he fell immediately after his next carry, which resulted in a five-yard loss on a sweep play across a slick field.

With their current record of 5-7, the 49ers find themselves at the bottom of the NFC West, trailing two wins behind the division-leading Seattle Seahawks and facing the possibility of missing the playoffs, a stark contrast to last season when they reached the Super Bowl only to be defeated by the Kansas City Chiefs.