Penarol coach Mario Saralegui has quit after his team lost 2-1 to Nacional in a friendly, the Uruguayan club said on Sunday.
The Uruguayan championship was suspended on Saturday for the second time in just over a month because of security problems.
The Uruguayan championship, suspended following a riot on the pitch at a game two weeks ago, resumed on Wednesday and immediately ran into controversy as Nacional beat Villa Espanola 2-0 to go top.
Supporters of Uruguayan clubs Danubio and Nacional fought on the pitch after the top-of-the-table match on Sunday which the hosts won 1-0.
The Uruguayan Football Association have called an indefinite halt to Apertura action following Sunday's riot after the match between Danubio and Nacional.
Penarol kept alive their chances of winning the Uruguayan title after coming from 3-1 down to beat River Plate 5-3 in a playoff after their opponents again collapsed in a big game.
Modest Danubio won the Uruguayan championship by beating Penarol on penalties following a 1-1 draw.
Uruguayan champions Nacional asked for Thursday's Copa Sudamericana match with Argentina's Boca Juniors to be postponed on Monday after being hit by a bout of mumps.