The Blues value Mata at £25m plus, but with boss Jose Mourinho having little faith in the Spanish star they are ready to let him play elsewhere in Europe until the end of the season.
PSG and Juventus are among the teams keen on the playmaker, but Chelsea will not let him join any of their Premier League rivals.
Despite being Chelsea's player of the year for the last two seasons, Mata's style of play has not suited Mourinho, who early on identified Brazilian Oscar as his No.10.
Mata, 25, knuckled down to try to impress Mourinho, who wanted him to be more involved when the Blues did not have the ball.
But the final straw was when he was hauled off after only 53 minutes of the 3-0 win at Southampton. He stormed off to the bench, clearly furious with Mourinho.
After the game, the Portuguese coach said he was ready to listen to offers for the ex-Valencia star.
While the Mata row rumbles on, keeper Petr Cech has backed £32m man Willian to inspire Chelsea to their first league title in four years.
Brazil star Willian, 25, came on to net his second league goal in the win at Saints. And he has a key role to play now, with Frank Lampard set to spend a month out crocked.
Cech said: "He's been brilliant. He keeps working, making the difference, scoring goals, defending. I thought I would never see anyone running more than Ram.
He keeps working, making the difference, scoring goals, defending. I thought I would never see anyone running more than Ramires, but he is.
"Questions were raised because he came from Anzhi, where he was unlucky with injuries, so didn't play much.
"From day one, he has worked really hard. He was waiting for his chance and you can see he is taking it.
"He can only get better in the second half of the season. You always give players a few months to settle because the Premier League is different to anywhere else."
