The Germany international has 18 months left on his current deal, with United boss David Moyes a known admirer having scouted the midfielder last week.
Kroos, who has been capped 41 times by Germany, is said to have already turned down one offer of a contract extension from the Bavarian club.
"I am unable to rule anything out," he told kicker-Sportmagazin.
"I am under contract with Bayern Munich (until June 2015). Actually there are yet no further talks (regarding a new contract) scheduled. I will therefore fully focus on the second half of the season.
"There are worse situations in life. I play for a top club, and under a top coach. I am pleased, and sometime in the future a decision will be made."
Kroos, who came through the youth set-up at Bayern, has made 118 appearances for the club and scored 12 goals.