On Wednesday morning, the Vikings stopped watching film of No. 2 quarterback Jason Campbell when the Browns announced they will start No. 3 quarterback Brian Hoyer. By Wednesday evening, the Vikings had to stop and change tapes again when the Browns traded their No. 1 running back, Trent Richardson, to Indianapolis and brought in former Broncos running back Willis McGahee for a physical.

"Without question, it definitely throws you a curveball," said coach Leslie Frazier, whose Vikings play the Browns in a game between 0-2 teams at Mall of America Field on Sunday. "You don't know how much watching the tape of what they've been doing the first two weeks will really matter. It creates some … you're not sure. You just have to have some good rules about what you're doing because you're probably going to have to adjust as the game goes on. It may not be what you saw on tape."

McGahee, 31, was signed Thursday. He's a nine-year veteran and a four-time 1,000-yard rusher, but his 2012 season was cut short when he suffered a torn medial collateral ligament and a compression fracture in his knee and lower leg. The Broncos released him in June, but he has passed physicals for three different teams and is reportedly in good enough shape to play on Sunday despite having no on-field work since his injury.

"That was a little different," Frazier said of the rare NFL in-season trade that sent Richardson to the Colts for a 2014 first-round draft pick. "We were watching tape and [Richardson] definitely was one of the guys we were preparing for from a defensive standpoint and then all of a sudden, he's not there. You got to be ready to adjust."

The Browns also have Bobby Rainey, an undrafted second-year player they picked up off the waiver wire from Baltimore, and fullback Chris Ogbonnaya. Neither one has carried the ball this year. Rainey has no NFL career carries while Ogbonnaya has 95 in five seasons.

Vikings defensive end Jared Allen joked about the unusual week of preparation, saying, "I've been trying to watch preseason tape of the quarterback and now I'm trying to throw darts at a board and see who the running back is going to be."

Allen said preparing this week has been tough, but he's assuming the Browns' offensive schemes will remain the same.

"It doesn't change how they're going to block up front and it doesn't change the fact that they're an effective running football team," Allen said. "They run a lot of downhill power game and they want to hit you in the mouth and that's a fun type of football game. People hear Trent's gone and you hear all the talk about them kicking it in for the season. That's not the case."

Actually, even with Richardson, the Browns weren't an effective running team this season, averaging 56 yards per game. But Allen says he's still wary.

"This is a humbling league," Allen said. "If you don't take every opponent serious, if you don't think someone can come in — I was reminding the guys that we didn't know who the Arizona running back was last year [LaRod Stephens-Howling], I think he ran for like a buck-fifty — so this is how this league stays successful because guys get an opportunity to shine and we just got to make sure no one shines on us."

Stephens-Howling ran for 104 yards and a touchdown on 20 carries (5.2 yards per carry) and caught four passes for 45 yards in a 21-14 loss to the Vikings at the Metrodome a year ago.

Ellison misses practice

Rhett Ellison, the tight end/fullback who would be Adrian Peterson's primary lead blocker at fullback with Jerome Felton serving the third and final game of his league suspension, didn't practice again Wednesday because of a knee hyperextension.

Ellison will need to practice at least on a limited basis Friday for him to be active on Sunday. If he doesn't play, undrafted rookie Zach Line will see his reps significantly increase.

"Zack would be the guy," Frazier said. "He's done a good job the first two games. And his snaps will probably go up a little bit because of Rhett's absence. But we got some other ways we can get things done."

Also limited in Thursday's padded practice were: NT Fred Evans (shoulder), MLB Erin Henderson (heel), FS Harrison Smith (shoulder), C John Sullivan (knee) and DT Kevin Williams (knee).

Etc.

• Backup safety and special teams player Andrew Sendejo signed a two-year contract extension.