The newly-promoted Ligue 1 side dropped their first points of the campaign in a goalless stalemate on Friday, which was played behind closed doors
Monaco's perfect Ligue 1 start was brought to an end on Friday as they were held to a goalless draw by Toulouse.
Claudio Ranieri's men had breezed past Bordeaux and Montpellier in their opening two encounters.
However, they laboured to a disappointing stalemate against Alain Casanova's side - who earned only their second point of the campaign - in a game played behind closed doors at Stade Louis II as punishment for crowd trouble at the end of last season.
Radamel Falcao again led the line, looking for his third goal of the season, with top scorer Emmanuel Riviere - scorer of a hat-trick against Montpellier - partnering him up front.
Riviere, who moved to Monaco from Toulouse in January - was the first to provide his former club with a scare after 11 minutes, dragging an effort wide of the far post being put through by Falcao.
The 23-year-old drew a smart save from Ali Ahamada just seven minutes later as Monaco dictated play, with Layvin Kurzawa and Lucas Ocampos both wasting chances to score shortly after.
Highly rated Belgian winger Yannick Ferreira Carrasco then spurned a golden opportunity to put Monaco in front, firing over from close range after Ahamada could only parry a low cross.
Toulouse midfielder Oscar Trejo forced Danijel Subasic into a fine stop just before the half-hour mark, but that proved to be their only real opportunity of the game.
Still, Casanova will have been pleased with his team's defensive effort, as the Garonne club stood firm until the interval.
Chances proved to be few and far between in the second half, Kurwaza's 53rd-minute effort failing to test Ahamada as Monaco struggled in their attempt to break the deadlock.
Attacking midfielder James Rodriguez was thrown into the fray by Ranieri after an hour, but it was Jeremy Toulalan who came closest to finding the winner, the former Lyon and Malaga man rattling the crossbar from 30 yards out three minutes from time.