The Trotters accepted Chelsea's offer of £7 million for the England defender earlier this month, but he has yet to rubber stamp a move to Stamford Bridge.
Talks regarding salary and the length of his Chelsea contract have been ongoing, and Andre Villas-Boas revealed the two parties had differing opinions over both aspects.
It is reported, however, that Cahill's transfer will be confirmed in the next day or so but, until then says Coyle, the 26-year-old remains a Bolton player.
"Dialogue continues between Gary's agent and Chelsea," he explained.
"We accept it has probably been long-drawn. It is over two weeks ago that we agreed a fee.
"But sometimes that is the nature of football business. It can take that period of time.
"Gary is a Bolton player and until I hear something different in terms of negotiations being concluded between both parties, he will be in line to play against Manchester United."