Asked if he would sell one of his best players to a rival, Chelsea boss Mourinho replied: "Yes. You see it happen in Italy every season without a problem.
"I don't know why it doesn't happen here. I don't think the old-fashioned mentality of 'I don't sell players to the clubs in the same country' helps the market.
"It doesn't help the players and sometimes you push players abroad when you should be interested in making sure they play in your league.
"When you keep players in your league, you are contributing to making your league the best. So when you want to sell and you push the players abroad, I think you are giving the wrong contribution to the league."
Mourinho used William Gallas as an example of letting an unhappy player leave to join a rival.
"I was so sad about Gallas because he was fundamental for us. But he want, he want, he want, he want to go and we couldn't stop him, so we decided NOT to stop him.
"As you know, in this club it wasn't an economical problem. The player just wanted to go. [Ricardo] Carvalho and [John] Terry were playing central defence all the time and he [Gallas] wanted to be first choice all the time."
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