Manchester United’s pursuit of their summer transfer targets is not proving straightforward, with Grêmio digging in their heels over Douglas Costa and Real Madrid providing stiff competition for the signature of Antonio Valencia.

As revealed by The Times on Tuesday, United have opened talks with Grêmio about signing Douglas, the Brazil Under-20 attacking midfield player.

Sir Alex Ferguson, the United manager, wants to take Douglas on a three-week trial this summer before deciding whether to make an offer for the 18-year-old, but that request was rejected by Duda Kroeff, the Grêmio president, who has told the Barclays Premier League champions to make a straight cash bid or end their interest.

Douglas is understood to have a release clause of about £21 million in his contract, which has four years left to run, but United are prepared to pay only about a third of that figure.

“I received a phone call from someone working for Manchester United,” Kroeff said. “He asked for Douglas to be released [for a trial] and said that he would not play, but that they wanted to see him in action. I said to them that this will not happen.

“Douglas is not at a stage where he would go through such a situation. He is an established player, he is not a stranger. He has no need to face tests at European clubs.”

Valencia’s future is expected to move closer to being resolved next week, with United and Real having lodged bids for the Wigan Athletic and Ecuador winger.

United may yet ask Real to step aside given that they are selling Cristiano Ronaldo to them. However, the Spanish club have been badgering Wigan for weeks about Valencia and have offered no indication that they are prepared to back off.

Valencia, 23, is thought to want to stay in England. He is concerned that his first-team opportunities might be more limited at the Bernabéu given Ronaldo’s impending arrival and the capture of Kaká from AC Milan.

Ferguson also admires Karim Benzema and Sergio Agüero, the Lyons and Atlético Madrid strikers respectively, both of whom are valued at about £45 million, but the United manager is not interested at the kind of prices being quoted.

United would be more tempted if Lyons or Atlético dropped their valuations to around the £25 million mark, but given that both players are only 21 and remain relatively inexperienced, Ferguson believes that even then a move for either would be a gamble.

Robert Kraft, the owner of the New England Patriots American football team and the New England Revolution, said yesterday that he decided against buying Liverpool in 2005 because of the absence of a salary cap in European football.

“I’d like to see a salary cap come to the English Premier League,” Kraft said. “If it did, I’d buy a team in a minute. I would be interested in other teams in the Premier League, but Liverpool was a unique franchise, with a great following. We came very close to buying it, very close.”