Sheffield United say that Christian Nade's move to Hull City collapsed after the Tigers changed the conditions of their offer for the French striker.
The 22-year-old was reported to have rejected a performance-related deal at the KC Stadium, but the Blades say that that is not the case.
Chairman Terry Robinson told the club's official website: "We are slightly bemused to hear reports that people have raised questions about Christian's level of fitness.
"Such levels differ from player to player and, although he is not a hundred yard sprint specialist, he is an impact player who scored three goals in the Premier League and another in the Carling Cup.
"Christian is as fit as anybody, with an impressive strike ratio given the outings he has made with us.
"The only reason that Christian refused Hull's deal is because the offer made to him by Hull in the end, was different to that originally offered by the Hull manager."