KANSAS CITY, Mo. — Baltimore Ravens coach John Harbaugh said he didn’t know the severity of quarterback Lamar Jackson‘s hamstring injury, which heightens the concern surrounding his club’s worst start in a decade.

Jackson left midway through the third quarter of Sunday’s 37-20 loss to the Kansas City Chiefs after being sacked by Chiefs defensive end George Karlaftis and he did not return. The two-time NFL Most Valuable Player sat on the bench for the remainder of the game, flexing his injured right leg occasionally.

“There’s nothing that looks like it’s season ending by any stretch for anybody,” Harbaugh said after watching five starters leave with injuries.

Asked if Jackson could have returned to the game if the score was closer, Harbaugh replied, “I really don’t have the answer to that right now.”

Jackson was not made available to reporters after the game.

Jackson’s injury came after Baltimore fell to 1-3, which has happened twice previously in franchise history (2005 and 2015). The Ravens failed to make the playoffs in each of those seasons.

Before the injury, Jackson recorded his worst performance of the season, struggling against Kansas City’s blitzes. After not turning the ball over in the first three weeks, Jackson threw an interception and fumbled when he ran into center Tyler Linderbaum. He was under duress on 56% of his dropbacks, which was the highest pressure rate he has ever faced in a game with at least 10 dropbacks, according to ESPN Research.

Jackson has proved to be durable in recent seasons. He hasn’t missed a game since he was sidelined for the final five regular-season games in 2022 with a knee injury. If Jackson can’t play Sunday against the Houston Texans, Cooper Rush will make his first start for Baltimore.

“Praying for Lamar,” Ravens safety Kyle Hamilton said. “I don’t know how serious it is, but we’ll see.”

In addition to Jackson, the Ravens watched four other starters leave the game with injuries and not return: middle linebacker Roquan Smith (hamstring), cornerbacks Marlon Humphrey (calf) and Nate Wiggins (elbow), and offensive tackle Ronnie Stanley (ankle).

The Ravens’ defense, which is allowing an NFL-worst 33.3 points per game, already entered Sunday’s game without four starters. Baltimore placed defensive tackle Nnamdi Madubuike (neck) and defensive end Broderick Washington (ankle) on injured reserve Saturday and made outside linebacker Kyle Van Noy (hamstring) and nose tackle Travis Jones (knee) inactive.

“Obviously, it sucks,” running back Justice Hill said of the mounting injuries. “Hopefully, they return quickly.”

Harbaugh said he’s “concerned but not overwhelmed” by the 1-3 start.

“The three losses are against probably three of the top teams in the league, for sure,” said Harbaugh, whose Ravens also lost to the Buffalo Bills and Detroit Lions. “That’s just the hand we’ve been dealt, but it doesn’t really matter. We’ve got to win the next game. Then, once you win the next game, then you have a chance to start stacking some wins. That’s what we’ve got to do big-picture-wise.”