Eddie Howe quit unexpectedly Newcastle United after a 4-1 loss to Bristol City, Sky Sports News said.
Sky aired his last interview soberly.
He briefly talked about the Bruno Guimaraes signing before walking out right after.
Former player Jay Bothroyd warned strongly the club could face danger of relegation without Howe.
Sky Sports will nationwide broadcast the premier Scottish Premiership opener on Saturday.
Dundee United welcome Rangers at Tannadice.
Manager Jim Goodwin firmly said he wants to make a statement there.
Dundee United coach Derek McInnes confirmed two United players are absent and several are uncertain.
Rangers look forward to Thelo Aasgaard and Cammy Devlin to be available for the match.