Le Havre, relegated to the French Second Division at the end of last season, have confirmed they will ask world governing body FIFA to investigate the case of Pogba, who they claim had agreed to join them, only to leave for United.
The case is similar to that of Premier League rivals Chelsea, who on Thursday were banned by FIFA from signing players until January 2011 for improper conduct when they acquired Gael Kakuta from French First Division club Lens in 2007.
A United spokesman told Reuters on Friday: "As far as we are concerned, we have followed acted within the regulations of both UEFA and FIFA in the transfer.
"We have nothing to fear as we have done nothing wrong. We know Le Havre are not very happy with us, but we have acted correctly."
However, Le Havre managing director Alain Belsoeur claims he has evidence proving United offered inducements for 16-year-old Pogba to join them and will include it in submissions to the world's governing body.
"We are still pursuing our case (with FIFA)," he was quoted as saying in The Times.
"It is a very serious case. We are confident that we will win because it is in the best interests not just of our club, but of the sport."
Pogba is one of the most highly-rated young players in France and has captained the under-16 national team, but is yet to have his registration cleared to play for United.
The allegations first arose at the beginning of last month when Le Havre accused United of offering very large sums to Pogba's parents to end his contract with the French club.
Le Havre claim United offered Pogba 3,500 pounds a week from when he turns 17 next March.
Chelsea are to appeal against their ban on signing players for the next two transfer windows after being found guilty of their behaviour in Kakuta's transfer.
