It emerged last week that talks had begun between the two Barclays Premier League sides over the sale of the England international, 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 this morning revealing that agreement over a fee - believed to be in the region of £7million - for the 26-year-old has been reached.
"There has been a fee agreed between the clubs and we have now given Gary's representatives permission to speak to Chelsea," said Coyle, speaking ahead of Bolton's New Year's Eve home clash with Wolves.
"That is where we are with it. 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.
"That is why they have representatives - to sort that out - and whatever January 1 brings, it will bring."
If Cahill, who joined Bolton in 2008 from Aston Villa, is to leave Wanderers in the next few days, Coyle will view it as a blessing that the move is occurring early in the January transfer window, giving him a chance to reinvest the money in new players.
The Trotters are currently 19th in the table and with Cahill departing, it would seem imperative that the squad - which has been blighted by injuries - is strengthened over the coming weeks if they are to avoid relegation.
Bolton have been linked with New York Red Bulls defender Tim Ream, who recently spent some time training with them, although Coyle will not be drawn at this point on the specific identity of any targets.
"There are a number of players out there who are of varying degrees of interest to us, and that is where we are," Coyle said.
"There are some good players and I think it is fair to say that we do want to add one or two to the group, but it would be remiss of me to start mentioning individual names.
"Those are players who belong to other teams and I have always tried to be very respectful of that."