The 24-year-old has been linked with Manchester United, Real Madrid and AC Milan.
McClaren told Sky Sports News: “At the present moment we’re not in control of it. He’s got a clause in his contract where he can go for a set fee before Monday.
“We’re really sweating on it. After Monday, if nothing happens, we take a little bit more control over the situation and we can dictate it a little bit more. He’s a world-class striker and we don’t want to lose him.
“We’re fighting tooth and nail to keep him. If we want to be successful we have to keep our best player, as every team does.”
