David Moyes travelled to Germany on Friday to watch the midfielder, and Brazil international Dante, in action with the 24-year-old's contract due to expire next year
The 24-year-old midfielder will be out of contract in June 2015, with talks over a new deal for the Germany international having stalled despite chief executive Karl-Heinz Rummenigge's eagerness to reach an agreement.
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Speaking to kicker-Sportmagazin, Kroos remained coy on his future, refusing to fully commit himself to the Bundesliga giants beyond the end of the current campaign.
"I am unable to rule anything out," he admitted.
"I am under contract with Bayern Munich. Actually there are yet no further [contract] talks 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."
The club-record £37.1 million purchase of Chelsea midfielder Juan Mata remains United's sole January buy although Moyes insisted at the Spaniard's unveiling that his arrival would be the first of many changes at the club.
Goal reported on Saturday that the Premier League champions had opened preliminary talks with Southampton over a £20 million deal for England Under-21 left-back Luke Shaw.