Adrian Peterson's thigh injury appears minor

MANKATO – The Vikings got a scare Tuesday afternoon when running back Adrian Peterson limped to the sideline after a collision on an inside run and later walked off the practice fields. But multiple sources later said that Peterson should be fine.

Peterson suffered a thigh injury after he burst through the line of scrimmage on a running play and tumbled to the ground after contact in the hole with defenders.

He quickly got up and limped to the sideline. A few minutes later, Peterson returned to practice for one play before departing for the trainer's room with head athletic trainer Eric Sugarman.

Peterson remained inside for the duration of practice, but Sugarman returned to the practice fields after spending several minutes inside with him.

After the practice, Vikings players, including Peterson's replacement with the first team, Jerick McKinnon, said they believed Peterson's injury was not major.

"He got tangled up," McKinnon said. "A defender fell on him, but he said he was all right. Everybody knows Adrian's got a cape on. He'll be back out here [Tuesday]. I don't think anybody's worried about him."

Two sources who confirmed McKinnon's amateur diagnosis did not give a timetable for Peterson's return to practice.

The 30-year-old back has missed seven games in his past four seasons, not including his suspension-shortened 2014 season.

Veteran cornerback Captain Munnerlyn did not play in Sunday's victory against the Pittsburgh Steelers in the preseason opener. Asked why, Munnerlyn told a reporter that's a question for coach Mike Zimmer.

Zimmer had already offered up his explanation for Munnerlyn's inactivity earlier in the day.

"We planned on him playing [in the nickel package] on third down and we didn't get any in that series," Zimmer said. "Then I pulled the rest of the guys out."

Sunday's game continued a trend in which Munnerlyn has often been spotted on the sideline with top pick Trae Waynes on the field in his place as the third corner. Munnerlyn missed most of the spring workouts because of a foot injury, but he said he feels perfectly fine now.

"I'll try to come out here and make plays," Munnerlyn said. "That's all I can do."

The versatility of tight ends Rhett Ellison and rookie MyCole Pruitt could convince the Vikings to go without a true fullback. Zimmer said "it's not critical" they have one.

"They have to earn their spot just like every other position," Zimmer said.

The Vikings carried two fullbacks for most of the 2014 season because they liked Zach Line, who returned Tuesday from a minor leg injury and is competing with rookie Blake Renaud.

Last season's starting fullback, Jerome Felton, played only 16.6 percent of the offensive snaps.

He did not participate in team drills, but it was a step in the right direction.

"We want him ready when we go to San Francisco [for the season opener], but we want to keep continuing to get him reps," Zimmer said. "He'll be all right."

Defensive end Justin Trattou has been making a positive impression on Zimmer, something that continued against the Steelers.

While Trattou did not record a tackle, he batted down a pass and was credited with six quarterback pressures by Pro Football Focus.

"He has improved a lot in almost all aspects," Zimmer said. "He's rushing the passer better. He's playing the run better.