Oxford United are keen to keep hold of winger Marvin Johnson amid interest from Leeds United.
He added that the final decision will rest with manager Pep Clotet, who was Leeds United's assistant last season.
Eales said: "Marvin is on a two-year, plus one-year extension, contract and unless someone comes in with some unbelievable offer, he will be at this club.
"The only way we would release Marvin is if Pep agrees to it and not me."
Clotet now has to look after his own team and not Leeds, and will have to consider Johnson's importance to the side.
Earlier this week he called out the winger, urging him to show greater consistency.
Clotet warned, via BBC Sport: "He's responsible for his own performance, the players who go somewhere are the players who perform week in, week out."
Johnson can play at left-back as well as in a forward role, and has been at Oxford just over 12 months after signing from Motherwell.