Borussia Dortmund defender Hummels and Bayer Leverkusen attacker Bender are both valued at around £25million, and the Premier League giants are ready to sanction a £50million investment on the pair of 23-year-olds.
Red Devils boss Sir Alex Ferguson sent chief scout Martin Ferguson to watch the pair in action for Germany in their goalless international friendly draw with Holland on Wednesday, and after receiving another glowing report is ready to step up his interest in both players in January.
Hummels signed a new five-year deal with Dortmund in the summer, but insisted on certain get-out clauses, and harbours an ambition to play in the Premier League.
Meanwhile, Bender penned a two-year extension in March to keep him at Leverkusen until 2017, but that is unlikely to prevent Manchester United from attempting to lure either player to Old Trafford.
"To play in a new country would be flattering," admitted Hummels. "I've had offers before from abroad and I have to admit that one of them was very interesting. But the timing was not right for me.
"When you are at a club like Dortmund you just don't move to any club and there are only four clubs in Europe I would consider."