Manchester United still hope they can beat neighbours Manchester City to the signing of Pep Guardiola and have significantly upgraded what had previously only been back-channel contact with the Bayern Munich manager, sources have told ESPN FC -- but there is concern they might have left it too late.

Despite widespread reports last week that United were giving full backing to Louis van Gaal, sources now say that was partly because it was close to a big Champions League game against Wolfsburg.

Defeat in that match and subsequent elimination from the competition, however, has caused doubt about the Dutch coach's suitability to the job to spread among the Old Trafford hierarchy. Saturday's 2-1 defeat at Bournemouth will only amp up the pressure.

There were always some who felt the club should be doing their utmost to bring in Guardiola, and that process has now been "greatly accelerated," a source said, with the prospect of the Catalan ending up at local rivals City also playing greatly on the minds of United officials.

The worry, however, is whether they are too far behind in the pursuit.

The friendship between Pep Guardiola and Sir Alex Ferguson could sway the Bayern boss to join Man United, sources say. GettyImages

Although Guardiola has given no indication to anyone over whether he will extend his stay at Bayern Munich, City have been working on signing him for three years, and sources say they are extremely confident they have done enough to secure his arrival once he leaves the Bundesliga.

Officials at the Etihad believe the opportunity to move the club onto a new level and do something "historic" greatly appeals to Guardiola, sources said. His pending arrival at City has been described as "the worst kept secret in football," reflecting the club's optimism in the situation.

A move to Old Trafford would involve a lot more work -- and potentially an overhaul of the squad.

There are many at United and at high levels of European football, however, who believe Guardiola is still enthused by the club's history and grandeur. The 44-year-old has reportedly brought up the subject at UEFA coaching meetings.