| 2021 Slovak Open II | |
|---|---|
| Date | 8–14 November |
| Edition | 23rd |
| Category | ATP Challenger Tour |
| Surface | Hard (Indoor) |
| Location | Bratislava, Slovakia |
| Champions | |
| Singles | |
 Tallon Griekspoor | |
| Doubles | |
 Filip Horanský /  Sergiy Stakhovsky | |
The 2021 Slovak Open II was a professional tennis tournament played on hard courts. It was the 23rd edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Bratislava, Slovakia between 8 and 14 November 2021.
| Country | Player | Rank1 | Seed |
|---|---|---|---|
 ITA | Stefano Travaglia | 81 | 1 |
| NED | Tallon Griekspoor | 88 | 2 |
 ESP | Carlos Taberner | 95 | 3 |
| SVK | Norbert Gombos | 110 | 4 |
| SVK | Alex Molčan | 114 | 5 |
 FRA | |||
 GBR | Liam Broady | 121 | 7 |
 CZE | Tomáš Macháč | 134 | 8 |
The following players received wildcards into the singles main draw:
Jonáš Forejtek Lukáš Palovič Lukáš PokornýThe following player received entry into the singles main draw as an alternate:
The following players received entry from the qualifying draw:
Danylo Kalenichenko Miloš Karol
Zsombor Piros Dalibor Svrčina The following players received entry as lucky losers:
Tallon Griekspoor def. Zsombor Piros 6–3, 6–2. Filip Horanský / Sergiy Stakhovsky def. Denys Molchanov / 
Aleksandr Nedovyesov 6–4, 6–4.
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