The 2023 Estoril Open (also known as the Millennium Estoril Open for sponsorship reasons) was a men's tennis tournament played on outdoor clay courts. It was the 8th edition of the tournament and part of the ATP Tour 250 series of the 2023 ATP Tour. It took place at the Clube de Ténis do Estoril in Cascais, Portugal, from 3 to 9 April 2023.
<sub>*per team</sub>
The following players received wildcards into the main draw:
The following players received entry as an emergency substitution:
The following players received entry from the qualifying draw:
The following pairs received wildcards into the doubles main draw: