San Francisco 49ers

Aaron Rodgers has a date with a 49ers jersey after losing a bet with the guys from Boyz II Men ... but the singers tell TMZ, they're willing to give him some time to prepare himself to pay up.

Singer Nathan Morris tells us, “Green Bay has another huge game [against the Bears] in 3 days so ... we understand where his head is, so I know he's focusing on that game.”

According to Nathan, Aaron promised to post the pic of himself wearing a 49ers jersey on his Twitter account if he lost against San Francisco ... which he did yesterday ... 30-22.

Nathan -- the biggest 49ers fan in the group -- is confident Aaron will hold up his end of the bargain, telling us, "Aaron might be one of the classiest guys we know.”

Green Bay Packers QB Aaron Rodgers has agreed to a deal that could land him in a 49ers jersey on Monday morning ... and it's all thanks to the guys from Boyz II Men.

TMZ has learned ... Rodgers and the R&B legends are actually friends ... and recently, Aaron asked the guys if they would sing the National Anthem at the season opener at Lambeau Field on Sunday.

But before the guys would agree to sing, Nathan Morris (the guy with the deep voice) had one MAJOR demand.

Turns out, Morris is a bigtime 49ers fan ... and proposed a friendly bet to the QB -- if SF wins, Rodgers MUST WEAR an Alex Smith 49ers jersey for the remainder of the week.

If GB wins, Morris has agreed to wear a Rodgers jersey.

A rep for the band confirms ... Aaron accepted the challenge and Boyz II Men agreed to perform at the game.

The stakes are pretty damn high for Rodgers -- considering SF passed on Aaron in the 2005 NFL Draft so they could pick up Alex Smith.

Plus, the Niners and the Pack are both considered NFC favorites this season.

So, we gotta ask ...

There have been multiple reports that the Oakland Raiders are the front-runners to acquire the Pro Bowl QB through a blockbuster trade -- but a source close to McNabb tells TMZ, "He does NOT want to play for the Raiders and would refuse the trade."

McNabb reportedly does not have a no-trade clause in his contract -- but according to Philly.com, he can refuse to negotiate a contract extension ... and most teams wouldn't trade away draft picks or players to get Donovan for the one measly year he has remaining on his current contract.