Cahill has been linked with a move to Arsenal all summer, but as yet no formal offer has been forthcoming.
The 25-year-old produced another impressive display in Bolton's 4-0 Premier League win at QPR, curling in the opening goal in first-half stoppage time from 20 yards.
Coyle does not know what will transpire over the closing two weeks of the transfer window, and a big offer could tempt the club to sell.
However, he feels Cahill can still take his game to another level with Wanderers.
"We will need to wait and see what the next few weeks holds before the transfer window closes. It would not be ideal for me to lose Gary, but I have always said, I need to be fair to Gary," said the Bolton boss.
"Any player wants to play at the highest level, to play the best teams, and there is nothing wrong with that.
"I have said to Gary he can improve here with Bolton, and he has improved.
"In the 18 months I have worked with him, Gary has become an integral part of the England squad because of his performances and has improved no end.
"There is no doubt he has taken his game to another level, but that was always going to happen with his age as well.
"Hopefully with the platform we can give him and encouragement as a staff we can help him on his way to a fantastic career."
Coyle added: "I am loathed to say this because he is my player, but if I was at one of those elite clubs, then Gary Cahill would be the first name on my shopping list."
While it will be business as usual for Bolton until such time as any official approach is lodged, Coyle accepts they will not be able to hold off suitors indefinitely.
"There has been no offer. He is my player and I have to make sure he delivers in each game," said Coyle.
"As a manager, I want the best players available for me, but I have also got to be fair to Gary Cahill as well.
"If it is the right thing for Gary and the football club, then that is something we have to look at.
"We are not one of the elite clubs who can be holding onto players, we have always been known as a selling club and that is not going to change.
"It needs to be the right business for everybody involved."
Coyle added: "There have not been any concrete bids, but as people get closer to the end of the window, and they think, 'He is the right one for me', then I don't know. You will have to ask the other managers."
Source: Team Talk
Source: Team Talk