| Date: | 10–16 May |
| Edition: | 7th |
| Draw: | 32S / 16D |
| Surface: | Clay |
| Location: | Heilbronn, Germany |
| Champs: |  Bernabé Zapata Miralles |
| Champd: |  Nathaniel Lammons / Jackson Withrow |
| Before Year: | 2019 |
The 2021 Heilbronner Neckarcup was a professional tennis tournament played on clay courts. It was the seventh edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Heilbronn, Germany between 10 and 16 May 2021.[1]
See main article: 2021 Heilbronner Neckarcup – Singles.
Bernabé Zapata Miralles def. 
Daniel Elahi Galán 6–3, 6–4.See main article: 2021 Heilbronner Neckarcup – Doubles.
Nathaniel Lammons / Jackson Withrow def. 
André Göransson / Sem Verbeek 6–7(4–7), 6–4, [10–8].| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Czech Republic | Jiří Veselý | 72 | 1 | |
| Yannick Hanfmann | 96 | 2 | ||
 Austria | Dennis Novak | 111 | 3 | |
| Colombia | Daniel Elahi Galán | 112 | 4 | |
 Japan | Taro Daniel | 114 | 5 | |
| Denis Kudla | 117 | 6 | ||
| Philipp Kohlschreiber | 119 | 7 | ||
| Mackenzie McDonald | 121 | 8 |
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 players received entry into the singles main draw as alternates:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
