Former Manchester United defender Rio Ferdinand says his old club must act to snap up Bayern Munich boss Pep Guardiola if he becomes available.
The Allianz Arena head coach is out of contract at the end of the season and will clarify his future plans after this weekend's Bundesliga match against Hannover.
Chelsea and Manchester City have been heavily linked with an approach for Guardiola, but Ferdinand does not want United – who recently crashed out of the Champions League in the group stages under Louis van Gaal – to miss out on a manager he thinks is the best in the world.
"The thing with Manchester United is that he will go to one Premier League team and won't be going to another [after that]," he told The Guardian.
"There is one chance – you have one chance to get him. He won't go to Manchester City and then to United; he is not going to go to Chelsea and then United.
"It won't happen, so you have got one chance to get the best manager on the planet. Is Guardiola better than what they have got? That is what United and City should be asking. If the answer is yes then you go for it, surely.
"It is like with the best players in the world – if someone like Cristiano Ronaldo or Lionel Messi becomes available, everyone is interested. I don't think it is different with a great manager.
"The best manager in the world is definitely Guardiola and when he becomes available people are going to be interested, and I think United are no different."
Ferdinand believes the United job is still hugely attractive despite the club's failure to win a trophy since Alex Ferguson's retirement in 2013.
"Every manager on the planet, probably bar the man at Manchester City, would love the Man United job," said the former England international.
"It is a huge job. Especially now, it is a job where, if you go in and do well, you will be seen as a hero – someone who has turned it around.
"It is a tantalising job. It is a job where you could create something with legacy. That is what Pep Guardiola likes to do, but he has got options.
"People talk about Man City, Chelsea, Arsenal. It is not going to be easy."
Former Barcelona boss Guardiola, 44, has won five league titles and two Champions League crowns since his first-team managerial career started in 2008.
