Roy Keane has held discussions with Celtic over succeeding Neil Lennon as manager.
And Sportsmail understands the Manchester United legend is one of a list of candidates the Parkhead club have already spoken to.
Red Bull Salzburg's American coach Jesse Marsch admitted he was 'honoured' to emerge as a target, while Manchester City under-23 coach Enzo Maresca and ex Sheffield United boss Chris Wilder are also interested. Scotland boss Steve Clarke has also been heavily linked with the role.
In a statement earlier this week largest shareholder Dermot Desmond vowed to take time to appoint the right man, insisting the process of 'research, investigation, interviewing and negotiation' is underway.
A Celtic player during the 2005-06 season, Keane has held discussions with senior figures leading the search.
His last frontline role in management at Ipswich Town a decade ago, the 49-year-old has since worked as assistant manager to Martin O'Neill with the Republic of Ireland, Aston Villa and Nottingham Forest.
Publicly backed by former Hoops boss O'Neill the outspoken Sky Sports pundit has moved to odds-on favourite for the post with bookmakers.
Rumours intensified after former teammate Nicky Butt quit Manchester United to pursue other opportunities.
It's now understood Butt's decision to leave Old Trafford was influenced by the elevation of colleague John Murtough - with whom he shared an uneasy relationship - to the role of Director of Football post rather than any imminent move to Glasgow.
Marsch, 47, was high on Celtic's list of potential managers and declared himself 'honoured' to be linked with the post. The American is now expected to remain in German football.
Keane's former teammate Keith Gillespie believes the Old Trafford legend would galvanise the Parkhead club after Steven Gerrard's title success at Rangers.
'They need somebody who is a name and I think it would be very interesting.
'If he does (join Celtic), you've got that rivalry of Gerrard and Keane, which adds a little bit more spice to it. But they're so far behind Rangers this season that they need something to change. think players will obviously respect him, they'll listen to him as a pundit. And so they'll know that he doesn't pull any punches.
'You'd like to think that the players would react and he's worked under Brian Clough, he's worked under Alex Ferguson. Two great managers.
'So you'd like to think that some of what he's learned off them will rub off.'
