Chelsea boss Luiz Felipe Scolari won't stop Alex quitting Stamford Bridge in January.
Scolari originally turned down Alex's request but has now decided he can go - for the right price.
A source close to Big Phil told The Sun: "Scolari doesn't like to work with unsatisfied players. If Alex wants to leave, he can. Whoever comes in with £15m can take him."
The Blues boss feels his authority is being undermined by a player who has no intention of staying.
And his decision to sell is also based on the quality he has already at the club.
The source added: "Alex is complaining because he wants to play. But his contract doesn't say he has to be a starter in the team.
"Scolari has Terry and Carvalho - a partnership he considers the best in the world.
"Alex thinks because he is Brazilian, the Brazilian coach will protect and play him which is not true."