Los Angeles Galaxy boss Alexi Lalas has warned Freddy Adu about the risks of making "the wrong move" overseas.
A wonderfully balanced dribbler, Adu has match-winning potential
Adu, 17, is training with Manchester United but Lalas is worried the Premiership might not be right for him.
"He is a wonderful talent but I worry about his size. He needs to go to the appropriate team," said Lalas.
"If he goes to the wrong team he will get swallowed up on and off the pitch - it will be a waste of time. He's not a player that can adapt to anything."
Adu, who plays for American team DC United, started a two-week stint with the Premiership leaders' Academy team on Monday, and Manchester United manager Sir Alex Ferguson has already expressed a desire to sign the teenager if he proves himself.
"I think we would be interested, he's only young but we have known of him for a long time," said Ferguson earlier this month.
"We tried to get him here some years ago but he signed for DC United and that stopped the progress of us keeping tabs on him."
Adu, who will be available for transfer when he turns 18 next June, has made clear his wish to leave Major League Soccer for a bigger challenge and a number of top European teams have been linked with the Ghanaian-born sensation.
"My ultimate goal is to go overseas and if it comes sooner rather than later I'll take it," said Adu after DC United's season-ending defeat to New England two weeks ago.
But former US star Lalas, the only American to play in Italy's Serie A, is concerned a move to a club of Manchester United's size is too much too soon for Adu.
This is a view supported by Adu's current manager, former Polish international Peter Nowak.
"I think he'd like to go to somewhere he's not only going to play but also develop in the right way," said Nowak, who was teenage sensation himself in Poland before moving to teams in Germany, Switzerland, Turkey and ultimately America.
"(But) I don't think the clubs with the highest budget in the world will wait for Freddy to develop - they can buy another player for $20m or $30m.
"They can do that and if you don't like it they're going to buy another player.
The 5ft 8in Adu (right) is training with Man Utd for two weeks
"The guys who really develop kids in the right way are the Dutch league and some of the Spanish league, because it is more technical.
"But the English league is very hard. And there are guys that cost $20m just sitting on the bench."
Adu, who is listed as being 5ft 8in, has been the subject of hype and speculation ever since he made a series of eye-catching performances in the US as a boy.
Born in the Ghanaian port of Tema, he moved to America aged eight when his mother won an immigration lottery. His family settled in the Washington DC area and word of his prodigious ability soon spread.
At 13 he joined US Soccer's full-time programme in Bradenton, Florida, and then at 14 he became the first player taken in the 2004 Major League Soccer draft.
Adu, still 14, became the youngest player to appear in US professional sports since 1887 when he made his debut for DC United on 3 April, 2004. Two weeks later he scored his first professional goal.
He was quickly signed up by Nike - Manchester United's shirt supplier - and featured in numerous advertising campaigns and computer games.
His arrival on the MLS scene prompted an unprecedented amount of interest in the sport in the US but the subsequent two years have been more mixed.
The top pick at 14, Adu has been in the media spotlight for three years
The left-footed teenager has enjoyed plenty of highs - 11 MLS goals, appearances for the MLS All-Star team and a first international cap - but there have been a few lows too.
There has been criticism that he is too young, too small and too attack-minded - some have even suggested he is older than his official age and has stopped growing - and he has clashed with his club over playing time and his position.
In three seasons with DC United, Adu has made 87 appearances, 59 as a starter, but has been largely used as a winger, not the more central, attacking midfielder role he craves.
Even his international future is not settled as his substitute appearance for the US in January has not ruled out a switch to his native Ghana.
But whatever doubts still surround Adu, there is no arguing with the fact that he is an exciting prospect on the pitch and eminently marketable off it.
It is perhaps the latter that will be most persuasive come next summer, particularly to an American-owned Premiership football team.