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Ben Leber admits facing Kyle Orton on Monday night will force the Minnesota Vikings defense to deal with the unknown to a large extent.

Orton hasn’t taken a meaningful snap as a Bears quarterback since Jan. 1, 2006, when Chicago finished the 2005 regular season against the Vikings at the Metrodome. That game, which also was Mike Tice’s swan song as Vikings coach, marked Orton’s 15th start of the season. But in Chicago’s 33 regular-season or playoff games since, either Rex Grossman or Brian Griese has been under center.

“I think it’s tough because it brings that realm of unpredictableness,” said Leber, in his second year as a Vikings linebacker. “I think with Grossman or Griese in there you have tape, you can understand how (they) are trying to attack defenses. With Orton we don’t know.

“They may come out and still try to run the football because that’s their personality, or they may say, ‘Hey, Orton is the best when we get him in the shotgun and he can sit there and throw the quick balls like he did at Purdue and throw the ball down the field.’… I think the first quarter and a half is going to be kind of a feeling out period.”

A three-year starter at Purdue before being taken in the fourth round of the 2005 draft, Orton had a 10-5 record as a rookie. Despite his record, Orton only completed 190 of 368 passes for 1,869 yards with nine touchdowns and 13 interceptions, a lowly 59.7 rating.

Orton lost the starting job to a healthy Grossman by the end of the season.

“I wanted the chance for a long time, I don’t think anybody should be judged on their rookie year,” Orton said of his return. “I think I can quarterback this team to a lot of points and play very effectively.”

Bears offensive coordinator Ron Turner is among those interested to see if that is truly the case.

“He hasn’t played for two years, so obviously he has got to get back into the flow of it and get the rhythm and all that stuff going,” Turner said. “I do expect him to play a lot better than how he played just because he’s a different player right now. …

“Physically, he’s different. Mentally, he’s different. He knows the system so much better. He’s going to go out and play well.”