Days after Di Canio expressed a wish to end his playing days with Celtic - as McStay has now been compelled to do after 15 years as a first-team mainstay - he accused McCann of breaking his word over contract negotiations and intimated that he could not continue to play for the Scottish runners- up under his stewardship.
McCann responded by condemning Di Canio's "despicable outburst", saying that the player was suspended by the club without pay for two weeks.
In an astonishing open letter to supporters, addressed to "my dear friends", the 28-year-old former Milan midfielder said: "Over the past few weeks I believe I have done everything professionally correct to save my relations with Celtic, and deliberately avoided making public the real problems between myself and Fergus McCann, whom I allowed the time needed to reflect on my situation.
"To this date I have received no reply whatsoever and I have come to understand that Mr McCann does not agree that I finish my career with Celtic, which is what I want with all my heart. The dream I thought I'd started to realise when I became captain is disintegrating before my eyes."
Di Canio added that it would "go against all my principles" to carry on playing for a club whose managing director did not keep financial promises. He also warned that potential signings would "think twice" before joining Celtic, while players would try to leave "as quickly as possible".
The internecine strife in Glasgow's east end has already seen Tommy Burns lose the manager's job at Rangers, while Jorge Cadete has also threatened to leave Celtic Park amid reports that his salary is half that of Andreas Thom.
All in all, it formed a tawdry backdrop to McStay's last day as a player at Celtic. The persistent ankle injury which limited his appearances during another season of under-achievement for his only club has now persuaded him to call a halt at the age of 32. McCann said that he would be offered a chance to stay on the staff.
McStay, a member of Scotland's squads for the World Cup finals of 1986 and '90, captained his country on many occasions. Fittingly, his 76th and last cap came at Celtic Park in March, when he appeared as a substitute in the victory over Austria.
Having made his Celtic debut in 1982, McStay gained three championship medals, although many observers argued that his lack of aggression and arrogance prevented him fulfilling his vast early potential.
Developments at Celtic overshadowed the announcement of Craig Brown's Scotland squad for the critical World Cup qualifier in Belarus on 8 June and the warm-up games against Wales and Malta.
Deprived of Colin Hendry, Alan McLaren and Colin Calderwood by injury and suspension, Brown called up Hearts' David Weir for the first time. Weir will be vying for a place in central defence with Christian Dailly and Brian McAllister, both also uncapped.
The Scotland manager said that he would give a first cap to Neil Sullivan, the Wimbledon goalkeeper, against Wales at Kilmarnock on 27 May or in Malta on 1 June. The Crystal Palace midfielder David Hopkin will join the squad for the first time after the First Division play-off final on 26 May.
Aberdeen's Scott Booth, who appeared in two of Scotland's matches in last summer's European Championship finals, is waiting to hear whether Borussia Dortmund want to sign him after his three-day trial with the European Cup finalists. Dortmund's coach, Ottmar Hitzfeld, said he had made "a good impression".
SCOTLAND SQUAD (Friendlies v Wales, Kilmarnock, 27 May and v Malta, Valletta, 1 June, and World Cup qualifier v Belarus, Minsk, 8 June): Leighton (Hibernian), Sullivan (Wimbledon), Howie (Motherwell); Boyd (Celtic), Burley (Chelsea), Collins (Monaco), Dailly (Derby), Dodds (Aberdeen), Durie (Rangers), Gallacher (Blackburn), Gemmill (Nottingham Forest), Hopkin (Crystal Palace), D Jackson (Hibernian), Lambert (Borussia Dortmund), B McAllister (Wimbledon), G McAllister (Coventry), McCoist (Rangers), T McKinlay (Celtic), Spencer (Queen's Park Rangers), McNamara (Celtic), Weir (Hearts), Whyte (Middlesbrough). (Burley, Hopkin and Lambert available for matches in Malta and Belarus only).Reuse content