Cahill has been strongly linked with Liverpool and Arsenal and Coyle has admitted he will not prevent the central defender joining one of the Premier League big guns for the right money.
No offers have been lodged for the 25-year-old but Coyle is braced for bids after Cahill impressed once again, scoring in his side's 2-0 friendly win over Bury on Wednesday night.
So solid: Defender Gary Cahill in Bolton's win over Bury on Wednesday
He said: 'I think it is well known the belief I have in Gary Cahill, the quality he has, but that's the nature of football.
'It only takes a phone call for it to all change but I have said to him he is a Bolton Wanderers player, he is well paid by Bolton Wanderers and he has to make sure he is focused to do the job in hand until something was to change.
'He is such an outstanding player that we are very fortunate to have him. I know there is interest from other clubs, nothing concrete in terms of offers, but all these elite clubs know he is an outstanding player so we will have to wait and see what happens with that.'
Coyle gave midfielder Nigel Reo-Coker his debut against the Shakers.
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