Gremio have ruled out allowing Douglas Costa to trial with Manchester United.

The 18-year-old Brazilian is a target for Sir Alex Ferguson, who had been keen to see the player in action before sanctioning an £18m bid.

United have been tracking Costa for some time and wanted to bring him to England for a 20-day trial period. However, Gremio's president, Duda Kroeff, has rejected the idea, insisting he is too good for such a proposal.

"We have said to them [Manchester United] that this will not happen," said Kroeff. "Douglas is not at the stage where he would go through such a situation."