The San Francisco 49ers season-long succession of quarterback injuries continued Sunday in the NFC Championship Game against the Philadelphia Eagles.

Starter Brock Purdy left the game in the first quarter with a right elbow injury but was forced to return in the second half when backup Josh Johnson was knocked out action with a possible head injury.

The 49ers listed Purdy as questionable to return. Johnson was shoved to the turf and the back of his head hit the ground hard, which brought Purdy back onto the field just four minutes into the third quarter. He handed off on the play before the 49ers punted.

The 36-year-old Johnson, who had started just nine times in a journeyman career, was being evaluated for a possible head injury after he had completed seven of 13 passes for 74 yards (no TDs or interceptions) and had been sacked twice.

Purdy was injured on the 49ers' sixth play from scrimmage when he was pressured by Philadelphia's Haason Reddick. The ball came out of Purdy's hands for a lost fumble just as Reddick was delivering a blow.

Purdy was examined on the sideline and started to go on the field for San Francisco's next offensive series with 4:50 remaining. He then returned to the sideline and was replaced by Johnson.

Johnson, who was a fifth-round pick of the Tampa Bay Buccaneers in the 2008 NFL Draft, was signed to the 49ers practice squad on Dec. 6, two days after Garoppolo broke his left foot. He has thrown just 355 passes in his career. He has a 1-8 record as a starter and has seen game action in 39 games with seven different teams.

During the regular season, Johnson completed one of two passes for 10 yards while mopping up against the Tampa Bay Buccaneers in Week 14.

Purdy, a rookie out of Iowa State, is a finalist for Rookie of the Year honors and is 7-0 as a starter. He took over for the injured Jimmy Garoppolo, who became San Francisco's starting quarterback again after Trey Lance sustained a season-ending ankle injury in Week 2.