The Reds have been left red-faced after mystery man Dexter Rosales failed to appear for a trial a week after the club announced it would look at the American alongside Sydney-based Portuguese product Fabio Ferreira as potential signings.

United coach John Kosmina is putting his squad through a tough pre-season camp in the Adelaide Hills this week, and it was expected that Ferreira and Rosales would take part.

Ferreira has linked up with the squad but there was no sign of Rosales on Monday, and understands club officials have now conceded they have probably been sold a dummy.

"It has been a strange few days with all the speculation around this mystery man - it doesn't look great from our end," a Reds media spokesman admitted tonight.

"We're not the first club to be given a false lead with a supposed trialist, but other clubs probably just don't promote it to the world like we did."

Former USA youth representative Rosales was said to have been a former player with top clubs like River Plate and Ajax and was being touted to Adelaide by a Sydney-based FIFA-registered agent.

But a closer inspection of his CV reveals massive holes in his backstory - and a Google check only reveals a string of dodgy self-created websites.

The 25-year old was said to have turned down a move to Valencia after an Achilles tendon injury ended his contract at Ajax and had instead returned to Miami in the US.

However YouTube videos showing him in action are actually of an entirely different player with a similar name.

And a picture of the mystery man and Klaas Jan Huntelaar at Ajax was supposedly taken three years after the Dutch legend had left the Eredivisie club.

Rosales had been linked with a trial at Western Sydney Wanderers in June when doubts first emerged about his existence.

And when Adelaide last week announced they would be trialing the mystery man, the rumour mill went into overdrive.

Adelaide's own players got wind of the situation and started joking about Rosales' phantom-like existence on Twitter.

Dario Vidosic, Sergio van Dijk, Bruce Djite and Jon McKain used the #IFoundDexter hashtag to post pictures of famous Dexters from the world of television. understands at least one other A-League club was forwarded Rosales' CV, but they decided not to pursue him when an internet search revealed a suspicious lack of information.

One A-League source admitted: "There are far too many doubts about his existence."

Officials at Ajax, Valencia and River Plate have also now dismissed any links with the player.

"Dexter Rosales was never a contracted player here at Ajax and never was on trial," an Ajax media official said.

"I checked Google and saw that there was a (picture) card with the name Dexter Rosales, but that picture of the player in the Ajax kit was Mauro Rosales.

"Mauro was a player from Argentina who was at the club until 2006, but the card and text is not 'Ajax official'.

"We do not know if Dexter Rosales does or does not exist, but we can confirm that he never was at Ajax."

Valencia also denied the player ever graced the Estadio Mestalla pitch.

"He was not a player of Valencia CF," a press official said.

And River Plate added confirmation to the rapid unraveling of Rosales' non-existent career.

"River Plate Athletic Club does not have any registration that says Mr Rosales was a former player," a media officer said.

The alleged player's Australian agent - Sydney-based Lou Nesci - directed enquiries to Rosales's international agent "Dimitri Kascovic"...but he too also appears to be a fake, and is not listed on FIFA's register of licensed agents.