The 2021 Rio Tennis Classic was a professional tennis tournament played on hard courts. It was the second edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Rio de Janeiro, Brazil from 13 to 19 December 2021.
The following players received wildcards into the singles main draw:
The following player received entry into the singles main draw using a protected ranking:
The following player received entry into the singles main draw as a special exempt:
The following player received entry into the singles main draw as an alternate:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
