If Brazilian signs, it will spell more bad news for Tottenham Hotspur and Villas-Boas
Jose Mourinho hints at Willian arrival at Chelsea
Spurs appeared poised to announce a deal for the Anzhi Makhachkala forward after he completed a medical, but Chelsea swooped in to forge a deal of their own, after making their long-standing interest known.
A deal was quickly agreed between the Blues and the Russian club - the respective owners Roman Abramovich and Suleyman Kerimov are friends and compatriots.
Willian has been keen to move to Stamford Bridge since first becoming aware of a potential switch to Chelsea two years ago.
"I think he's already made his decision," Mourinho said.
The coach nodded in the affirmative when asked if that was Chelsea.
He added: "I don't like to speak before time because football can be crazy. I know what the player wants, so in this moment we cannot hide that it's a possibility."
Willian is still to undergo a medical at Stamford Bridge, but if he signs it strikes a blow for Mourinho over his former staff member Andre Villas-Boas, once of Chelsea and now the Tottenham manager.
Losing out an the attacking player could also stiffen Spurs' resolve to attempt to keep Bale from a move to Real Madrid.
Mourinho understands the need for medicals before contracts being agreed, but also spoke of the danger of a deal being trumped by another club. "The best thing to do is to do the medical in secret," he said. "After that when you sign the contract with the club and the player, you say 'done'."
Mourinho had insisted the Manchester United striker Wayne Rooney was his sole target, but revealed he had alternative options, too.
Willian is "an extra target", said Mourinho, who plans a third bid for Rooney following Monday's Premier League clash at Old Trafford.
Mourinho added: "I couldn't say much in previous press conferences. I have to answer your questions and try to be honest, but at the same time try to hide a few things.
"I'm happy with my squad, but every one of us managers, we say we are happy, but we are always unhappy. We always want something of more quality and we never close the door to the possibility of adding more quality."
Mourinho anticipates departures, but only temporarily.
"If somebody's coming, somebody will leave," he said.
"The point is not to sell. I want a 22-player squad. If somebody comes, somebody leaves.
"Do we need to sell? No, we don't. Do we need to loan? Probably, yes.
"I don't like to work with big squads. I like to work with a small group of players and I think 22 is the perfect number to answer to our needs in four different competitions."
The Willian move was unexpected as the one Anzhi Makhachkala player reported to have been on Mourinho's radar was Samuel Eto'o, who played under the Portuguese at Inter Milan.