It was Mourinho who signed Willian during his time at Chelsea in 2013 after he snubbed a move to Spurs, where he did have a medical.
Willian brought an end to his seven-year stay at Stamford Bridge and opted to join cross-town rivals Arsenal on a free transfer.
However, Mourinho admits the North London side were unable to pay Willian's wages.
"We don't have money for Willian," Mourinho said when asked whether he explored the option of signing a player that he knows well.
"We cannot pay the wages that he gets at Arsenal, so I didn't want to waste our time because we cannot pay these wages.
"He is still dangerous, he is still one of the best players in the Premier League.
"Apart from that, he is a good friend. I have nothing to hide in relation to that. We keep in touch, we keep in contact, we call each other.
"We wish good things to each other. He is my friend and of course he is a very good player."