Cahill was below par on Saturday as Bolton lost to Liverpool.
“I don’t think Gary performed at his maximum. It is natural for a young player to have his head turned by all the transfer speculation,” said Coyle.
“I can’t really use the word offer about Arsenal but there was a verbal conversation last week. There has been no dialogue since then but we have to wait and see where we are at the close of play on Wednesday.
“It is hypothetical but if something happens with Gary and he goes, we would then need to bring in someone to replace him. We signed Dedryck Boyata on loan from Manchester City last week but that is not connected to Gary’s situation.”