Cahill has established himself as one of the Premier League's best centre-halves over the past couple of seasons and has been rewarded with England honours.
He has been linked with a summer move away from the Reebok Stadium and the likes of Arsenal, Chelsea, Manchester City and Tottenham Hotspur are all rumoured to be admirers.
However, Coyle insists the former Aston Villa youngster remains a Bolton player and feels Cahill may be getting frustrated by the constant rumours about his future.
"Gary has been the subject of speculation every day, probably to the point he is frustrated by it," said the Bolton boss.
"I have been very open. Some of the elite clubs in this country have noted their interest.
"But there has been nothing concrete. Until that changes, Gary is a Bolton player."
Meanwhile, Coyle is on the hunt for at least one more striker given Johan Elmander and Daniel Sturridge have both departed this summer.
Shaun Wright-Phillips and Robbie Keane are both believed to be on Bolton's radar, although Coyle claims there is nothing to report.
He added: "We have been trying to bring one or two in, and we will continue to do that."