Speaking to The Bolton News, Coyle confirmed that a handful of top clubs had contacted chairman Phil Gartside about Cahill, but no firm offers have been received.
"There's been clubs making known their interest to Phil but nothing hard and fast," he said.
"Gary could play for anyone, and I really mean that, so if I'm honest I'm a little bit surprised there hasn't been anything.
"Looking across the marketplace and a few of the deals that are going on at this moment in time, it does surprise me that there hasn't been that concrete offer.
"But people have to take their time and make sure they come up with the right offer because he certainly won't be going on the cheap, that's for sure."