Eagles offensive tackle Lane Johnson is in the concussion protocol after leaving Sunday’s game against the New England Patriots with a head injury.

Coach Doug Pederson announced Johnson’s status during his Monday news conference. The 29-year-old right tackle left between drives in the second quarter and was replaced by Halapoulivaati Vaitai.

It’s unclear what exactly caused Johnson’s injury, but there were a handful of plays in which Johnson made helmet-to-helmet contact during the Eagles’ 16-play, 95-yard drive in the first half.

“He’s in the protocol,” Pederson said. “He came out after that touchdown drive. I don’t know specifically what the play was, but it was after that drive that he came to the sideline and we checked him.”

The Eagles’ offense missed Johnson greatly. The seven-year veteran has made two Pro Bowls and was named to the 2017 All-Pro team. He’s been graded as the NFL’s best run-blocking tackle this season by Pro Football Focus, and his absence was felt in the final 43 minutes of the 17-10 loss.

With Johnson on the field, the Eagles averaged 4.7 yards per carry. They didn’t allow a sack and had a balanced attack, running the ball 10 times and throwing it eight times.

With Johnson out, the team threw 33 passes and had 11 called runs. Carson Wentz was sacked five times, including one that resulted in a fumble. The running game sputtered as well, as the Eagles averaged only 3.1 yards per carry en route to the second-worst rushing performance the team has had all season.

Losing Johnson "affected the run game a little bit,” Pederson said. “From the standpoint of him and Brandon [Brooks, right guard] working together and getting those reps during the week. Still got a lot of confidence, obviously, in Big V; he filled in there. But it’s a loss. You’re talking about a Pro Bowl-caliber right tackle, and he and Brandon together do some great things, so it affects you a little bit.”

Pederson said Johnson is in “stage 1” of the protocol but didn’t have any other specifics on the severity of the injury.

The Eagles will play the Seattle Seahawks at 1 p.m. Sunday and would likely turn to rookie tackle Andre Dillard if Johnson isn’t able to clear the protocol in time to go.

The 24-year-old out of Washington State spent three games as the team’s starting left tackle while Jason Peters recovered from a knee injury that required arthroscopic surgery. Dillard played well but relinquished the starting job once Peters was back.

Pederson said Dillard had spent the previous week in practice still getting reps at left tackle as Peters worked his way back into the fold, but he said Dillard would be with the starters at right tackle this week in case Johnson won’t be available.

“Moving forward, depending on Lane’s status at the end of the week, the plan will be to work Dillard in at right tackle,” Pederson said.