Guardiola is the hottest property in football after revealing he will be leaving Bayern Munich at the end of the season.
The former Barca boss has already agreed terms with City, who plan to axe Manuel Pellegrini at the end of the season.
But though those terms are in place, both United and Chelsea have made contact this week and been told to come back with a firm offer.
It leaves Guardiola in an astonishing position of having the pick of three of the Premier League’s biggest clubs who would all love him to choose them.
But it also leaves City sweating on whether their hard work and planning behind the scenes over the past few months has been a waste of time.
Guardiola has gained a reputation for leaving it until the last minute before making a decision, and City find themselves in a dangerous position with Pellegrini knowing he is a dead man walking.
United have been long—term admirers but were caught napping by City going for Guardiola two months ago, and officials at Old Trafford had feared they were too late.
But they have sounded out Guardiola’s representitives this week and been told there is no paperwork signed with City, giving them some hope they can still get him to choose them.
Yet the fear of losing out on Guardiola is weighing heavily on the minds of the Glazers and Ed Woodward, and the availability of Jose Mourinho has thrown up another conundrum.
For if they keep faith with Louis van Gaal now, spurning the chance to get Mourinho, and also miss out on Guardiola then the United board would be ridiculed by the club’s supporters.
Chelsea have time on their sides after appointing Guus Hiddink as interim manager following Mourinho’s departure last week.
Roman Abramovich has targeted Guardiola before but the Spaniard has always had reservations about working for the Russian billionaire because of his reputation for sacking managers.
He is prepared to offer more money than City to get his man, and will stump up the cash for a major squad investment programme if successful.
City are now pressing Guardiola to put pen to paper, but his camp know the ball is in their court with so many potential suitors.