Owen Coyle, the Bolton manager, on Friday confirmed the clubs had agreed a fee for the England international.
It emerged last week that talks had begun between the two Premier League sides over the sale of the defender, 26, who is out of contract at the end of the season and has for some time been linked with a move away from the Reebok Stadium.
And it seems a deal is now imminent, with Coyle revealing that agreement over a price - believed to be in the region of £7 million (Dh40.25m) - has been reached.
But Villas-Boas said: "We're still miles apart regarding agreement with the player. We'll continue to monitor this situation as we continue to monitor others."
The Portuguese manager was confident, however, an agreement would eventually be reached and hailed the qualities Cahill would bring to Stamford Bridge.
"Gary has been this season involved in a fighting struggle with Bolton and a fight for position in the league," he said. "I think his technical attributes are immense. His pace is fantastic, as well. There are weaknesses and they are also related to the collective weaknesses of Bolton.
"He's a player that, at international level, has been playing well. "He can add to this squad or any squad in the Premier League."
Coyle meanwhile expects Cahill to give his all for Bolton until a deal with Chelsea is confirmed.
"We obviously have a game tomorrow and I have said to Gary that he has to be focused on giving everything for Bolton Wanderers, because he knows Bolton Wanderers has been terrific for him just as much as Gary has been for us," said Coyle.
"That is why they have representatives - to sort that out - and whatever January 1 brings, it will bring."
Villas-Boas said midfielder Josh McEachran would not be joining Bolton on loan but could move to another club.
Chelsea are also reported to be considering breaking the British transfer record for the second time in a year by moving for Brazil forward Hulk. Villas-Boas is said to be mulling a fresh attempt at prying Hulk away from Porto, who have placed a €100 million (Dh480m) buyout clause on the player.
Chelsea have lacked thrust in attack with Fernando Torres, who cost a record £50m in a move from Liverpool in January, struggling to find form, and Didier Drogba leaving to play in the African Cup of Nations.