Eyre told the Scunthorpe Telegraph: "I approached Scunthorpe to see if I could train with them but they turned me down.
"But I'm due to spend a couple of weeks training with Darlington and I genuinely believe I've still got two or three good years left in me."
Iron boss Brian Laws admitted that taking Eyre on could have proved a risk.
He said: "I know John really well but didn't think it was right for him to come here and train with us.
"We had to think of the insurance side of things too. He's a player out-of-contract, so if he got injured our backs wouldn't be covered."