The England defender is out of contract in the summer so the Trotters must sell in January or risk losing their prize asset on a free in the summer.
Chelsea boss Andre Villas-Boas this week confirmed his interest in the 26-year-old, while Arsenal and Manchester United have also been linked with the former Aston Villa man.
And although Coyle suggested Cahill's departure is imminent, he is confident he will continue to give his all to Bolton's survival bid as Wanderers face Newcastle and Wolves before the window opens.
"It's fair to say there's interest in Gary, and there will be," Coyle told Sky Sports News.
"That doesn't surprise me. I've said from day one I believe Gary Cahill can play for anybody, I think he has those qualities.
"There is serious interest in Gary, but I've got to say we have two huge games before 1st January, before anything could happen.
"More than his ability, he's an outstanding man, and because of the lad he is, his focus will be doing the best for his team-mates, who he's stood shoulder to shoulder with for years here, and trying to help them get points in these two games. Then whatever January brings, so be it.
"There's nothing signed and sealed at the moment but it's fair to say there has been dialogue. I've got to be up front and tell you, as I always do, and that's the situation."
Cahill cost £5million from Villa in January 2008 and is expected to fetch around £7m this January.
And should Bolton agree a fee for the sought-after defender, Coyle intends to reinvest the money to boost his depleted squad ahead of a potential relegation scrap.
He added: "We know, given the injuries and suspensions we've had, that we need two or three (new players) to give us a fresh impetus to kick on in the second half of the season.
"There's business to be done and come 1st January, we'll see what happens. I think it's fair to say it'll be an interesting month."