The starting quarterbacks for the defending NFC and AFC champions suffered injuries on Sunday that forced them to leave their respective games. Carolina Panthers quarterback Cam Newton left the team’s Week 4 game against the Atlanta Falcons with a concussion, and Denver Broncos quarterback Trevor Siemian hurt his non-throwing shoulder.

Running for a two-point conversion with 11:42 remaining in Sunday’s game, Newton was hit by Atlanta’s Deion Jones as he reached the goal line. The quarterback didn’t return to the game and was diagnosed with a concussion following Carolina’s 48-33 loss.

Newton appeared to have a clear path to the end zone before he slowed down and was leveled by Jones. It might have been only a matter of time before Newton suffered an injury that would force him out of a game. He’s been hit more than any quarterback in the NFL this season, and he faced plenty of pressure on Sunday.

There was some controversy surrounding Newton in the season opener against the Broncos. He was sacked three times and suffered multiple blows to the head, but he was never taken out of the game and put in the concussion protocol.

It’s too early to know if Newton will be able to play in Week 5, though the quarterback does have an extra day to recover since the Panthers are set to face the Tampa Bay Buccaneers on “Monday Night Football.” Newton hasn’t been sidelined since 2014, and the two games he missed during that season mark the only starts he hasn’t made since being drafted in 2011.

Derek Anderson threw for 172 yards, two touchdowns and two interceptions in relief of Newton on Sunday. He’d get the start if Newton can’t go next week.

Siemian left the Broncos’ game against the Tampa Bay Buccaneers late in the second quarter. He was carted off to the locker room after being sacked for the third time on Sunday. 

Rookie Paxton Lynch replaced Siemian, seeing the first action of his career. The quarterback led the Broncos on a field-goal drive when he entered the game, giving Denver a 17-7 lead at halftime. Lynch started the second half under center, though Denver said Siemian is available if need be.

Siemian has been a pleasant surprise for Denver, going 3-0 as Peyton Manning’s replacement. But he did struggle in the team’s first two victories, and the Broncos view Lynch as their quarterback of the future.

After winning the NFL MVP award in 2015, Newton ranks near the bottom of the NFL with a 78.0 passer rating. Carolina has already lost two more games than they did last season, and they trail Atlanta by two games in the NFC South.

Neither Siemian nor Lynch had ever attempted a pass before this season, but Denver looks to be a top Super Bowl contender. The Broncos are one of three remaining unbeaten teams.