Monaco had been in mid-table before surging into contention on a run of nine consecutive victories and they looked set to make it 10 in a row as they came from behind in Lens to lead 2-1 thanks to goals by Benoit Badiashile and Wissam Ben Yedder.
But Ignatius Ganago struck in the sixth minute of injury time to earn Lens a draw and deny Monaco, who finish third and will have to come through two qualifying rounds to make next season's Champions League group stage.
They missed out on a place in this season's group stage after losing a play-off to Shakhtar Donetsk in Ukraine.
