Allen won't return to Sunday's game against the Giants due to a left ankle injury, Adam Schefter of ESPN reports.
Allen was rolled up on when he was sacked by Jabrill Peppers late in the first quarter, with the latter incurring an unnecessary roughness penalty on the play. The severity of the injury isn't yet known, but Allen will finish the day 5-for-7 passing for 62 yards. Alex Smith has entered in Allen's stead and will have to finish the contest because second-year QB Dwayne Haskins was a healthy scratch.