The San Francisco 49ers’ worst fears have been realized. Star quarterback Jimmy Garoppolo has indeed suffered a torn ACL in his left knee and is out for the rest of the season.

Garoppolo suffered the injury late in the fourth quarter of Sunday’s matchup against the Kansas City Chiefs. His left knee buckled without contact as he was trying to cut back inside while scrambling near the sideline for more yardage.

After the game, 49ers head coach Kyle Shanahan admitted that they feared Garoppolo tore his ACL on the play. An MRI on Monday confirmed their suspicions.

It’s a tough blow for Garoppolo, who just signed a five-year, $137.5 million deal in the offseason. He made a dream start to his 49ers career as he won his first five starts at the tail-end of last season following his midseason arrival from the New England Patriots.

Through three games this season, he had completed just under 60 percent of his passes for 718 yards with five touchdowns and three interceptions as the 49ers got out to a 1-2 start.

Garoppolo joins running back Jerick McKinnon, the 49ers’ marquee free-agent acquisition who also suffered a torn ACL before the start of the season.

With Garoppolo out, the 49ers will now turn to C.J. Beathard as their starting quarterback moving forward. a third-round pick by the 49ers last year, Beathard appeared in seven games last season and made five starts.

He went 1-4 in those starts, as he completed 55 percent of his passes for 1,430 yards, four touchdowns, and six interceptions.