Folarin Balogun picked up an embarrassing yellow card as he made his Monaco debut on Saturday.
The American striker signed for the Ligue 1 side from Arsenal this week.
Monaco were already 3-0 up against Lens when Balogun was introduced with 72 minutes on the clock.
Wilfried Singo, Aleksandr Golovin and Guillermo Maripan had already scored for the hosts in cruise control.
It allowed manager Adi Hutter the luxury of resting Wissam Ben Yedder and sending on Balogun to make his debut following his move from Arsenal.
Balogun was instantly involved in the action, wanting a penalty after rounding goalkeeper Brice Samba.
The forward went to ground under the slightest touch but no spot-kick was given and Balogun was handed a yellow card for diving instead.
