MINNEAPOLIS -- Vikings fans were holding their breath Sunday when quarterback Sam Darnold went down with an apparent injury and then left the field. They exhaled when he returned after missing just one play, but it's unclear how extensive the injury is.

While Darnold finished the game, both he and head coach Kevin O'Connell indicated after the game that further testing is needed.

"We'll evaluate it, we'll look at it, but felt good enough to be able to go back in the game," Darnold said.

"He got rolled up a little bit on the penalty there, kind of low on him. He checked out and came back in the game," O'Connell said. "We'll go through an evaluation just to rule anything out, but was proud of Sam coming back in the game and helping take us down the field."

When asked whether his injury would keep him from practicing this week or playing Sunday against the Green Bay Packers, Darnold said, "I'm not sure."

O'Connell is expected to speak to the media Monday afternoon and could provide an update then.

Darnold's injury came late in the third quarter when former Viking Danielle Hunter hit him low. Hunter was flagged for roughing the passer on the play.

"Obviously [Hunter's] a great player, and not a dirty player whatsoever," Darnold said after the game.

Backup QB Nick Mullens came in for a play while Darnold got his left knee examined. Then, Darnold jogged back onto the field, buoyed by an ovation from the crowd at U.S. Bank Stadium.

"The fans' reaction meant everything to me," Darnold said. "Not only that, but my entire time here in Minnesota has been amazing with the fans."

Darnold's solid play has been a key part of the Vikings' 3-0 start. In Sunday's win over the Houston Texans, he threw four touchdowns and no interceptions. He's first in the league in touchdown passes, second in passer rating and fourth in adjusted net yards per attempt and QBR.

The Vikings already lost one quarterback for the season. Rookie J.J. McCarthy tore his meniscus in his first preseason game and was placed on injured reserve after a successful surgery. Aside from Mullens, the Vikings also have veteran Brett Rypien on the roster.