Chelsea manager Jose Mourinho has told Manchester United they will harm the Premier League if they refuse to sell striker Wayne Rooney to a domestic rival.
Rooney has been the subject of two unsuccessful bids from Chelsea in recent weeks and Mourinho has used the issue to stir the pot ahead of his side's clash with United at Old Trafford on Monday.
United manager David Moyes has repeatedly iterated that Rooney is "not for sale", but Mourinho believes the champions are wrong to be preoccupied about arming a rival for the title.
"That old-fashioned mentality of 'I don't sell players to the same country' doesn't help the market and doesn't help the players," he said, in comments reported by several British newspapers on Sunday.
"You see in Italy, it happens every season without any problem. The player wants to move from Milan to Inter, from Inter to Milan, from Roma to Juventus, from Juventus to Inter, and they do this all the time.
"From the big ones I think only (Francesco) Totti stayed all his life (at Roma). (Andrea) Pirlo -- Inter, Milan, Juventus.
"Sometimes you push players abroad when you should be interested in keeping them in your league, because when you keep players in your league, you are contributing to make your league the best league.
"So when you want to sell and you are pushing the players abroad, I think you are giving the wrong contribution to the league where you are."
Mourinho also questioned the wisdom of holding onto an unhappy player against his wishes, amid widespread reports in the British media that Rooney has grown disillusioned about his status at United.
He cited examples from his first spell at Chelsea, between 2004 and 2007, when both Arjen Robben and William Gallas were allowed to leave the club.
"We had Robben unhappy, we sold him to Real Madrid because he wanted so much to go to Real Madrid," Mourinho said.
"We had William Gallas unhappy, we sold William Gallas to Arsenal."
However, the Portuguese conceded that "every case" was different and he also admitted that United had not given Chelsea a glimmer of hope in their attempts to sign Rooney.
"We are going to get a maximum of two players in this transfer window," he said.
"If we get the second piece, it will be the final piece. Let's see. We make the bid and they say 'no' again; what do we lose? One email.
"The two answers we got from Manchester United were: 'We don't accept the bid, we are not interested in selling the player.'
"That's the only official contact we have had. It is the same till Monday. We have nothing else we would like to add to it and we want to respect them and football."
Chelsea announced on Sunday that they have agreed to sign Brazilian attacking midfielder Willian from Anzhi Makhachkala, in a deal reportedly worth £30 million ($47 million, 35 million euros).