Chelsea emerged as a potential bidder for Wayne Rooney after manager Carlo Ancelotti said he would be interested in signing the England striker should he become available.
Rooney's future at Manchester United appears to be in doubt after a reported breakdown in relations with his manager Sir Alex Ferguson.
Manchester City is widely reported in the British media to be ready to make an offer for Rooney but Chelsea is the first club to openly declare an interest.
"You have to see if Wayne Rooney really wants to leave," Ancelotti said on Monday ahead of Chelsea's Champions League match against Spartak Moscow.
"Secondly, if Manchester United really want to sell him, and thirdly if Rooney is on the market, I think that not only Chelsea but a lot of teams would be interested."
Ferguson is likely to be asked questions about his relationship with Rooney at a pre-match news conference at Old Trafford on Tuesday, ahead of United's Champions League game against Bursaspor.
Rooney started on the bench on Saturday as United drew 2-2 with West Bromwich Albion in the English Premier League, only going on with 19 minutes left in the game. That decision by Ferguson increased the speculation about Rooney's future.
British newspapers were united Tuesday in saying Rooney, who has less than two years left on his United contract, would be open to a move to City, following in the footsteps of Carlos Tevez. The Argentina striker made the cross-city switch to Eastlands in July last year.
The Times newspaper reported that Rooney has requested a 100 per cent pay rise to stay at United.
United chief executive David Gill said Monday the club would "say something [about Rooney] at a more appropriate time."