After returning from a three-game suspension, Vikings WR Jerome Simpson had an immediate impact on the offense, but he was slowed Sunday by weakness in one of this legs and the team isn't sure what's wrong. (US Presswire)

The Jerome Simpson era in Minnesota finally started last week in Detroit and then hit another snag Sunday in the Metrodome. After returning last week from his three-game suspension for violating the league’s substance abuse policy and making an impact in the game against the Lions, the wide receiver showed up Sunday for the game against the Titans with weakness and numbness in his leg. He spent much of the game on the bench, and the team still hasn’t figured out what was wrong.

“They’re running some tests this morning, so we’ll have a little bit better idea as the day goes on, with the MRI,” coach Leslie Frazier said Monday. “We think there could possibly be something connected to the back, as well as the leg."

Simpson showed up at the Metrodome on Sunday with the issue and then did pregame warmups in front of a cadre of team officials: Frazier, head athletic trainer Eric Sugarman, offensive coordinator Bill Musgrave, receivers coach George Stewart and even GM Rick Spielman. He caught passes from backup QB McLeod Bethel-Thompson as team officials watched. Simpson couldn’t push off very well, and, as a result, was used only marginally in the game.

“[He] just woke up in the morning with numbness, some weakness,” Frazier said. “[He was] fine when he was walking but just had a little trouble pushing off on it. We were hoping as time went on he would regain that feeling during the course of the game. 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.”

Frazier said that it had never happened to Simpson before and there was no tracing it back to any incident.

"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 Minnesota's win over the Lions last week, Simpson was able to show his value by catching four passes for 50 yards and drawing defensive penalties. The sooner he returns, the better it will be for the Vikings offense.

For more Vikings news and notes, follow Joe Oberle on Twitter @CBSVikings.