The following are the seeded players. Seedings are based on ATP rankings as of August 23, 2021. Rank and points before are as of August 30, 2021. As a result of pandemic-related adjustments to the ranking system, players are defending the greater of their points from the 2019 and 2020 tournaments. † Because the 2020 tournament was non-mandatory, the player was defending 150 points from his 19th best result instead of 90 points from the 2020 US Open. ‡ The player was also defending points from one or more
2019 ATP Challenger Tour tournaments. Those points were frozen in 2020 as a result of pandemic-related adjustments to the ranking system. § The player did not qualify for the tournament in 2019 or 2020 and is defending points from a
2020 ATP Challenger Tour tournament (
Ostrava) instead. ^ Because the 2021 tournament was non-mandatory, the player substituted his 19th best result in place of the points won in this tournament.
Withdrawn players The following players would have been seeded, but withdrew before the tournament began. ^ Because the 2021 tournament was non-mandatory, the player substituted his 19th best result in place of zero points for this tournament. ==Other entry information==