The 2021 ATP Lyon Open (also known as the Open Parc Auvergne-Rhône-Alpes Lyon) was a men's tennis tournament played on outdoor clay courts. It was the fourth edition of the Lyon Open and part of the ATP Tour 250 series of the 2021 ATP Tour. It took place in the city of Lyon, France, from 15 May through 22 May 2021. Second-seeded Stefanos Tsitsipas won the singles title.
<sub>*per team</sub>
The following players received wildcards into the singles main draw:
The following player received entry as an alternate:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
The following pairs received wildcards into the doubles main draw:
The following pair enters with a protected ranking into the doubles main draw: