Butcher takes over 'Well post
Former England and Rangers star Butcher was previously number two to Black.
Club chairman John Boyle has also put the club up for sale, sparking what will be a period of real turmoil for the SPL club.
Black has been strongly linked to join Coventry as Gary McAllister's number two, and is expected to be confirmed in this position in the next few days.
Black - with Butcher as his assistant - took over as Motherwell boss in October and, though they lie second-bottom of the SPL, has ensured their safety in the Scottish top flight.
The 'Well boss is rumoured to have been disillusioned that their young star Jamie McFaddon could be heading for Celtic.
After working successfully as Celtic's youth team boss, Black has a reputation for bringing the best out of young talent, and Coventry will hope he is similarly successful with their fledgling stars.
Butcher, who has previously managed at Coventry and Sunderland, takes over temporary charge of the club along with reserve coach Chris McCart.
Nevin's departure has come as something of a surprise, as the former Chelsea winger has had a large influence on affairs at Fir Park.
He joined the club from Kilmarnock in 1998, initially combining playing duties with his role as director of football at the club, before retiring at the end of the 1999/2000 season.
