A magnetic resonance imaging exam on Vikings wide receiver Jerome Simpson revealed a back issue that triggered numbness in his right leg and limited his participation against the Tennessee Titans, according to a person with direct knowledge.

More tests are necessary to pinpoint the problem, which flared when Simpson woke up before Minnesota’s 30-7 victory Sunday, Oct. 7, at the Metrodome.

Simpson, whom the Vikings planned to feature in their passing attack against the Titans, informed the training staff and coach Leslie Frazier that he could walk fine but was unable to push off or generate power with his leg during a pregame workout. Visibly frustrated on the sideline throughout the game, Simpson did not have a catch and only was thrown to three times by quarterback Christian Ponder.

“We were hoping as time went on he would regain that feeling during the course of the game,” Frazier said Monday. “In talking to the doctors they felt like that was possible. And it did get a little bit better but not to the point where he felt completely comfortable.”

Simpson returned to the Vikings’ lineup Sept. 30 at Detroit after serving a three-game suspension to start the season. He practiced without incident last week and was unable to trace the source of the injury.

“I asked him that when we were on the field and in my office at the stadium,” Frazier said. “This has never happened to him before. This was completely new to him. So as you can imagine it scared him, had him alarmed. But we’ll learn more over the course of the day.”

It is uncertain whether Simpson will be able to practice this week in preparation for Sunday’s game at Washington.

“From everything I’ve been told we shouldn’t be afraid to the point we’re going to lose him for a long period of time,” Frazier said. “But everything’s not conclusive as we speak.”

In other injury news, running back Adrian Peterson suffered a mild left ankle sprain on the Vikings’ initial series but recovered fine to gain 88 yards on 17 carries. It was the same leg he suffered torn anterior cruciate and medial collateral ligaments last season, and Peterson acknowledged being tentative upon his return.

“He played with confidence and he ran hard,” Frazier said. “There were no runs where you looked at and said, ‘Man, he’s favoring that leg or he’s not running as hard as he was running before.’ To his credit, he shook it off and played well.”

The coach was asked whether Peterson would be limited this week in practice.

“We’ll see how he does when we get back in on Wednesday and start practicing. We’ll try to be smart in terms of how we use him in practices,” Frazier said.

Meanwhile, Marvin Mitchell said he would resume practicing and should be fine to play against the Redskins.

And safety Andrew Sendejo, who has missed two games because of an injured ankle, is scheduled to resume practicing this week as well, according to Frazier.

Follow Brian Murphy on twitter.com/bmurphPiPress.