Cristiano Ronaldo has informed Manchester United he would like to return to the club one day, probably to end his career, after a summer in which the Premier League champions have explored the possibilities behind the scenes of bringing him back from Real Madrid.

United have been closely monitoring Ronaldo's position for the best part of a year and, while that has not resulted in a hard offer, their clear information is that he is open to the idea of moving back to Manchester, albeit not for at least one more season. The expectation at Old Trafford is that he will shortly commit himself to a new contract that recognises his status as Madrid's outstanding player, despite the impending arrival of Gareth Bale from Spurs for a world-record transfer. However, United are encouraged by the clear messages they have received about his affinity for the club and consider what he says to be genuine. Their information is that, realistically, they think he would be tempted to spend possibly the last three or four years of his professional life in Manchester. They are aware, however, that a move for him will not be simple by any measure.

A more determined attempt to re-sign him is feasible next summer, ahead of a season when he will turn 30, although there is also an acceptance that it is never going to be easy persuading him to leave Madrid, or his club to agree to letting him go. As well as sharing the stage with Lionel Messi as one of the two greatest players in the world, Ronaldo's value to Madrid in a marketing and commercial sense is immense. The Premier League champions are, however, prepared to look into it and, crucially, they are not put off by the vast sums of money that would be involved. They have also retained strong links with the player's agent, Jorge Mendes, despite Sir Alex Ferguson's retirement at the end of last season. Ferguson and Mendes are particularly close and the former United manager had made no secret of his desire to make Ronaldo feel more wanted in Manchester than he is in Madrid.

This drip-drip approach even involved strategically leaving Ronaldo's name to last – ensuring he attracted the biggest cheer – when the stadium announcer went through the two sides before Madrid's Champions League tie at Old Trafford last season. At the time, it was seen as a ploy to distract Ronaldo just before the game started.

It was actually Ferguson's idea and intended to have two purposes, one being to remind their former player of his enduring popularity in Manchester at a time when senior United figures had already started delving into his position at the Bernabéu. Ronaldo's assertion last September that he was "sad" in Madrid had accelerated the process and his relationship with José Mourinho had broken down by the end of last season. That Mourinho is no longer at the Bernabéu clearly works against United, as does the fact Ferguson is not around to add to his influence.

If there is a reservation, it is the underlying sense that Ronaldo enjoys being courted and will relish the knowledge he is wanted back by the club that let him go for £80m. With that in mind, United are keeping an open mind about when it might or might not happen. The key facts are that they will pursue it and have been informed Ronaldo is keen for it to happen.

Yet, to take the most cynical view, it is not lost on them there is a risk of being used as a way for Ronaldo to strengthen his own position in Madrid. United's view is that for a player of this importance they at least have to investigate.

One certainty is that, financially, they would need to push out the boat far more than they have in David Moyes's first summer in the job. United have had a frustrating and complicated transfer window, failing with bids for their top target, Barcelona's Cesc Fábregas, as well as becoming locked in a public disagreement with Everton over their "derisory" offer for Leighton Baines and Marouane Fellaini.