The move stunned the former United defender, who concedes that Bordeaux failed to make the most of the 20 year-old's talent, even shunting him out to Lorient on-loan for the second-half of last season.
"I was surprised, but it is an unexpected chance for him to play with one of the best clubs in the world," said Blanc.
"He has the potential, but he must overcome psychological and mental challenges so he can express his true value."
With a championship under his belt, Blanc can afford to shrug off the loss of Obertan, while at £3 million, the deal represents no great gamble for Ferguson, particularly after raising £80 million from selling Cristiano Ronaldo to Real Madrid.
On the face of it, Blanc's opinion rings true.
As he put pen to paper on his deal with Lorient in January, observers regarded Obertan's career at the crossroads. And after a disappointing six months, where he managed only a handful of starts, the player returned to Bordeaux with his tail between his legs and openly admitting he may have to drop out of Ligue 1 to kickstart his career.
"I have two years left on my contract with Bordeaux and we'll see what happens in preseason. I do not know what they expect of me," he said at the end of last season.
"I need games, I need to play a full season without asking any questions. I want to become a player in Ligue 1, but I also know that, for me, this will take a great effort. The talent is good but without the work, it does not lead to anything."
Where everything changed for Obertan was in a one-off U21 friendly against England. Despite his Lorient struggles, Obertan was outstanding against the Three Lions, scoring in the 2-0 win. Weeks later, he was named France's best player for the Toulon Tournament, leading the home nation to the final, where they were eventually beaten by Chile. In Toulon, Obertan displayed all the qualities which had him regarded as a future star at 16.
At 6ft 1in he boasts a similar physique to Ronaldo and has all the tricks in his locker to match. His pace, aerial threat and eye for goal were all on display and it was enough to convince Ferguson to move for him.
"It is a fairy tale, but I am aware that it will be very difficult to make it," says Obertan. "It will take time, it will also require me to be mentally sturdy, I know I need to work very hard.
"They had been following me already when I was 16 years old.
"Things accelerated in late March, when I played in England with Team France. Alex Ferguson contacted Laurent Blanc and my agent.
"When the opportunity arose, I did not hesitate. Some may think it's too early. But I do not think so. I am ambitious."
There's great similarities between Obertan and another Frenchman whose signing was questioned upon arrival.
Like Obertan, Patrice Evra was regarded as a wonderkid as a teenager, wanted by Europe's biggest clubs. But when he eventually moved to United, he was at the tail end of the poorest run of form in his career. Ferguson had virtually no competition for the then AS Monaco fullback, but he knew the qualities and character of Evra and had no hesitation signing him in January of 2006.
Three years on and Evra is regarded by many as the best left-back in the game.
Obertan will be a project player for Ferguson. There'll be no instant impact from the Clairefontaine graduate and Ferguson will be careful with his progress.
"I met the manager when I signed my contract," recalled Obertan. "He told me he wanted me, he believed in me, but that it was for me to prove myself.
"I will do everything not to disappoint."