Sir Alex Ferguson's right-hand man at Old Trafford for all but one of the last six years, Queiroz on Friday night agreed a four-year contract with the Portuguese Football Federation to succeed new Chelsea boss Luiz Felipe Scolari.

The 55-year-old's departure leaves Ferguson needing to find a new assistant manager with the club about to kick off their pre-season preparations at Aberdeen on Saturday.

But, perhaps more importantly, it removes a crucial link between United and Ronaldo, who covets a move to Real Madrid.

Queiroz is believed to have been instrumental in bringing Ronaldo to Old Trafford in 2003, as well as the club's other recruits from Portuguese football, Anderson and Nani, last summer.

He will now manage Ronaldo at international level and the winger is delighted at the appointment.

"I have been working with him for some time and I just have to say that he is very good for this job," he told Portuguese broadcaster RTP.

Whether Queiroz is still as committed to dissuading his star player from moving on remains to be seen.

He certainly has his own horror story to tell, having spent one unhappy season as Real boss in 2003-04 before returning to United as Ferguson's number two.

After four successful years at Old Trafford, he admits leaving is a wrench, despite feeling the time is again right to strike out on his own.

"It is with a very heavy heart that I leave the greatest football club in the world," said Queiroz, who will take full responsibility for all aspects of Portugal's national teams, including oversight of the youth teams.

"This has been a special period in my life both personally and professionally.

"To Sir Alex, I thank him for his faith in me and his knowledge, spirit and desire from which I will take strength and have confidence in my new role."

Ferguson was full of praise for his departing assistant, adding on www.manutd.com: "Carlos is one of the best coaches in world football.

"His attention to detail, ability to innovate and will to win have been a key factor to the team's recent successes. He has played an important role in building and blending the exceptional squad of players at the club."

FPF president Gilbert Madail expressed his gratitude to United for releasing Queiroz from his contract, saying: "I also want to recognise the co-operation of Manchester United from the beginning of this process."

Queiroz, who is to be presented to the media on Wednesday, added that his first priority will be qualification for the 2010 World Cup in South Africa.

Ferguson must now decide who to appoint as replacement for the high-rated Portuguese coach.

Former United stars Mike Phelan and Brian McClair are already on the coaching staff at Old Trafford, as is Dutchman Rene Meulensteen, and they could take on extra responsibility in the short-term.

Other candidates include Bordeaux coach Laurent Blanc, the former France defender who spent two seasons with United at the end of his career and Pako Ayesteran, Rafael Benitez's former number two at Liverpool.