The 25-year-old England international has been linked with the likes of Liverpool, Manchester City and Arsenal. Having seen Blackburn's England Under-21 star Phil Jones join Manchester United in a deal which could be worth £20million, Coyle is well aware of the value of his centre-back.
"I believe he could play for any club - I'd put my reputation on it," said the Scot.
"There's been a lot of interest - and you don't have to be a genius to work out some of the top clubs in this country have been interested - but nothing concrete yet. It would take a lot of money. It is up to those clubs to put something firm to the chairman.
"He is not a player we want to lose, I have to stress that, but we have to accept if it is the right deal for the club and the player it has to be done and that then frees up cash for us to invest in the club. I would love him to stay. He is a fantastic player for the club and I am not saying I want him to go, but if he does it will be the right business for the club."
If Cahill were to leave, likely for a fee in excess of £15million, Coyle is keen to plough that money back into bolstering his squad.
The Bolton boss has made considerable progress since taking over in January 2010 but is keen to push on further. He accepts, however, the club have to be on the ball with their transfer business if they are to stand a chance of beating rivals with bigger budgets to their targets.
"I am in the market to improve the club and I am looking to make sure we get the right quality to add to the squad and take the team forward," Coyle added.
"We have to make sure when we have targets we are first on the scene for them because if we arrive at the same time as Chelsea or Manchester United we will lose out. There comes a time when you are a manager when you need some help and finances might need to be made available.
"Hopefully we can add. There has been tremendous progress as we were a team favourites for relegation when I joined. We hope to have a couple of new faces in by the time we start pre-season on July 4."
Source: PA
Source: PA