Watford have announced the signing of Italy international Marco Motta, subject to international clearance.
Mark Noble has signed a new deal with West Ham which will keep him at the club until the summer of 2020.
Spurs appeared poised to announce a deal for the Anzhi Makhachkala forward after he completed a medical, but Chelsea have now hijacked the deal after making their long-standing interest known.
A deal was quickly agreed between the Blues and the Russian club - respective owners Roman Abramovich and Suleyman Kerimov are friends - and Willian has been keen to move to Stamford Bridge since first becoming aware of a potential switch to Chelsea two years ago.
He will also have the prospect of Champions League football, something Spurs were unable to offer.
"I think he's already made his decision," Mourinho said.
The self-styled Special One 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 Tottenham boss.
It could also hinder the prospective sale of Gareth Bale to Real Madrid, Mourinho's former club.
Mourinho had insisted 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 Barclays Premier League clash at Old Trafford.
Mourinho added: "I'm happy with my squad, but every one of us managers, we say we are happy, but we are always unhappy.
"We never close the door to the possibility of adding more quality."
Mourinho anticipates departures, but only temporarily and Juan Mata will not be among them.
Mourinho said: "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.
"Juan is not a player we want to lose. He's a player we all want to keep.
"We want more quality in the team, we don't want less quality."
The Willian move was unexpected as the one Anzhi player reported to have been on Mourinho's radar was Samuel Eto'o, who played under the Portuguese at Inter Milan.
Eto'o is possibly still an alternative target to Rooney.
Chelsea have been told repeatedly that Rooney is not for sale, but still Mourinho is chasing his man.
Asked how he rates Chelsea's chances of signing Rooney, Mourinho said: "I don't care. In this moment I don't care.
"I have a big match to play on Monday. I don't care about new players."