Jose Mourinho has compared attempting to sign Barcelona star Neymar to "trying to break into a safe".
There have been rumours of Manchester United triggering the 200million euros (£173million) release clause in the Brazilian's contract at the Nou Camp but Mourinho poured cold water on the story.
He told ESPN: "It's speculation. I always try to be objective and pragmatic with clubs and to ask them what they can give me. To ask for Neymar is absurd.
"A club like Barcelona cannot and will not lose Neymar. Although Messi is still a young player with years ahead of him, he's almost 30, and Neymar will be the great player of Barcelona post-Messi.
"So much that I think it (trying to sign Neymar) is like trying to break into a safe; impossible."
United return to action after the international break with a clash against West Brom at Old Trafford on Saturday.
Mourinho was left counting the cost of the break after Chris Smalling and Phil Jones picked up injuries on England duty to join Paul Pogba on the sidelines.
And Mourinho criticised the European qualification system for the World Cup, comparing it unfavourably with South America.
He said: "The European qualifiers make me angry. The South American qualifiers excite me. I enjoy football taken seriously, not for fun.
"In the South American qualifiers, there are a lot of good teams, on similar levels. Even those who aren't as strong as the others find some way to create difficulties.
"In Europe, the qualifiers are a joke. We qualify and who doesn't goes straight to the play-offs, where there is a brutal difference between the teams. In South America, the qualification stage is a true competition that lasts two years."
Mourinho, meanwhile, said he wanted an easier job after United when asked if he would be interested in coaching the Brazil national team.
Brazil became the first side to qualify for the 2018 World Cup after beating Paraguay on Tuesday.
Mourinho said: "I think after Manchester United I need an easier job, and coaching the Brazilian national team would be harder. Obviously it would be great, any coach would want to work in the best teams and national teams.
"There is a coach inside every Brazilian. In every journalist, there is a coach better than the coach. I think it must be a country that's hard to work, but also exciting. But I recognise that the Brazilian national team is for a Brazilian coach."
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