Paris Saint-Germain failed to capitalize on second-placed Lille's 1-1 draw at Reims to claim the Ligue 1 title beforehand, collecting a 2-2 tie with Strasbourg at home in the 31st round match of Ligue 1 on Sunday.
Choupo-Moting needlessly deflected a goal-bound shot from team-mate Christopher Nkunku onto the post from point-blank range to prevent his side going 2-1 in front in the first half.
PSG coach Thomas Tuchel chose to leave Mbappe on the bench until the 59th minute, a surprising decision especially after the league's top scorer found the net in his seven previous league matches, and in the absence of injured forwards Angel Di Maria, Neymar and Edinson Cavani.
Choupo-Moting was starting his latest match in the place of superstar Kylian Mbappe, and the World Cup victor reached out to his red-faced teammate following the astonishing miss.
"I hesitated to get the ball and asked if I was offside - it all happened really fast".
Strasbourg then moved 2-1 ahead before Thilo Kehrer rescued a point for PSG with eight minutes remaining in the French capital.
However, that was not enough for them to bag full points, as Tristan Dingome teed up Remi Oudin's goal 12 minutes from time.
Choupo-Moting had given the champions-in-waiting the lead after 13 minutes before Nuno Da Costa's leveller.
Thomas Tuchel's side will now have to wait until next Sunday's game away at Lille to seal their sixth title in seven years.
Although PSG dropped points, it will matter little in the long run as they are 20 points clear of their nearest rival in the league.
You may think that there is no earthly defence for such ineptitude, but Choupo-Moting still did his best to exonerate himself after the game.
He was replaced by Mbappe after 60 minutes with his side a goal behind and chasing the game.