Unbeaten Marseille have gone top of the French league even while failing to make the most of an extra man in drawing 1-1 at Nantes.
Marseille are one point ahead of Monaco, who enjoy a better goal difference and need only a draw at home to Lens on Saturday to reclaim first place.
Sarr was then fouled by 17-year-old defender Bastien Meupiyou, who was shown a straight red card in the ninth minute.
Veteran striker Pierre-Emerick Aubameyang missed an injury-time chance for Marseille, who finished third last season.
Nantes just avoided relegation and have only two points from four games.