Eddie Howe quit suddenly Newcastle United after a 4-1 loss to Bristol City, Sky Sports News said.
Sky aired his last interview briefly.
He briefly talked about the Bruno Guimaraes signing before walking out immediately.
Former player Jay Bothroyd warned strongly the club could face danger of relegation without Howe.
Sky Sports will live broadcast the national Scottish Premiership opener on Saturday.
Dundee United welcome Rangers at Tannadice.
Manager Jim Goodwin confidently said he wants to plant a flag there.
Dundee United coach Derek McInnes stated two United players are absent and several are in doubt.
Rangers hope Thelo Aasgaard and Cammy Devlin to be in form for the match.