After taking a look at Jimmy Garoppolo's knee injury on Sunday, the 49ers feared that their star quarterback had torn his ACL, and now what they feared has been confirmed.

The team announced on Monday that Garoppolo will miss the rest of the 2018 season after tearing his left ACL in San Francisco's 38-27 loss to Kansas City.

The injury came near the end of the game on a play where Garoppolo probably could have run out of bounds. On a third-and-goal from the Chiefs' 20-yard line, Garoppolo took off on a scramble with just under six minutes to play in the game. Once he got about 10 yards downfield, the 49ers quarterback had a chance to get out of bounds, but instead, he tried to gain a few more yards and that's when the injury happened. Garoppolo's left knee appeared to buckle just before he took a hit from Chiefs defensive back Steven Nelson.

After the game, Chiefs' pass rusher Justin Houston said Garoppolo only has himself to blame for the injury.

"That was his fault," Houston said of Garoppolo trying to gain a meaningless extra yard or two. "I pray he's not hurt, nothing serious, but as a quarterback you should step out of bounds. It was only an inch. That inch wouldn't have made a difference. You got the yardage you need, you step out of bounds. You got to be smart."

Before the injury happened, Garoppolo had thrown for 251 yards and two touchdowns in the game. The injury is devastating news for the 49ers, who signed Garoppolo to a five-year, $137.5 million deal during the offseason. The former Patriots quarterback won the coaching staff over in 2017 after winning five straight games to close the season.

Thanks to Garoppolo, the 49ers had high hopes heading into 2018 despite a 6-10 record last year. The 49ers went 1-2 this season in his three starts. With his year now over, Garoppolo will finish the 2018 season with 718 passing yards, five touchdown passes and three interceptions.

The 49ers will now move forward with backup quarterback C.J. Beathard as their starter. The 2017 third-round pick out of Iowa appeared in seven games for the team last season with five starts (1-4). During his time on the field, Beathard completed 54.9 percent of his throws for 1,430 yards, with four touchdowns, six interceptions and a passer rating of 69.2.