BOSTON (CBS) – San Francisco 49ers quarterback and former Patriots backup Jimmy Garoppolo left Sunday’s game against the Kansas City Chiefs with what the team fears is a serious knee injury.

Tom Brady’s former understudy was scrambling trying to reach the first down marker in the fourth quarter.

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Garoppolo took a big hit up high, but the damage appeared to be a non-contact injury before he took the hit. He left the field on a cart.

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Head coach Kyle Shanahan told reporters after the game the team fears Garoppolo tore his ACL.

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Trainers were looking at his left leg on the sidelines before Garoppolo left the field.