There has only been one public declaration so far, from businessman Sir Jim Ratcliffe, and there is uncertainty about interest in the Premier League club from Qatar.

Who has bid so far?

Despite suggestions that United have not attracted the interest expected by their owners, insiders have told BBC Sport the process has proceeded positively.

As they stated in their announcement on a potential sale in November, the Glazer family are still considering "all strategic alternatives" for the club, which could include new investment or other transactions involving the company.

Lifelong United fan Ratcliffe, one of Britain's richest men, is said to be determined in his interest and is understood to have employed the services of banking giants JP Morgan and Goldman Sachs to help him.

However there is a growing feeling a Qatari bid will be launched, even though this would be complicated.

What would a Qatari bid look like?

A final round of bidding was initially planned for March by the US-based Raine Group, which has been put in charge of finding new owners or investors.

Paris St-Germain president Nasser al-Khelaifi is set to be a key figure in any Qatari ownership bid, even if he could have no direct involvement in the club.

Qatar Sports Investment (QSI), headed by Al-Khelaifi, had been looking at the potential for taking a smaller stake in a Premier League club, which would be allowed under Uefa rules that prevent multi-club ownership. QSI already has a minority stake in Portuguese side Braga.

However, given QSI's ownership of PSG, which it has no interest in selling, any Qatari move to buy United in its entirety would have to come through private individuals or a different organisation.

This could potentially be the Qatar Investment Authority - a global investment platform that includes London department store Harrods and the UK's largest building the Shard in its portfolio.

Even that may require European governing body Uefa to change its rules on dual ownership, given it is felt by many that all Qatari funds are distributed from a central source.

Al-Khelaifi could therefore be key in helping any bid proceed.

Why is Al-Khelaifi key?

Al-Khelafi, 49, took a more prominent position in football's political circles when he refused to hitch PSG to the European Super League bandwagon.

That decision is viewed as one of the major reasons why Uefa was able to resist the plan.

Since then, Al-Khelaifi has taken over as chairman of the European Clubs' Association and has developed a close relationship with Uefa president Aleksander Ceferin.

It is regarded as impossible that any Qatari bid for United could be being put together without his knowledge.

United and PSG are not in the same competition this season, so any amendments to Uefa regulations to allow Qatari ownership at Old Trafford would not need to be activated until the end of July. It would then have to be approved by Uefa's executive committee.