The Argentine overcame Yuichi Sugita on Tuesday in his first ATP event since the Miami Open in March, but withdrew on Wednesday afternoon upon hearing the news of his grandfather’s passing.
Del Potro, a two-time champion in Estoril, was set to play American Ryan Harrison in the last 16, but has headed back to Argentina to be with his family.
Raducanu: Be a little patient with me
The news comes days after fellow ATP player Nick Kyrgios withdrew ahead of the tournament to attend his grandfather’s funeral in Australia.
Murray beats world No.10 Hurkacz to reach Vienna Open second round
Murray aiming to be 'more clinical and ruthless' in Vienna