Iker Casillas reported for pre-season duty for Porto on Monday just two months on from a heart attack.
The 38-year-old suffered a myocardial infarction in training on May 1 and underwent emergency surgery before returning home five days later.
The former Real Madrid captain was pictured arriving at Porto's training ground on Monday as the Primeira Liga side began preparations for 2019-20.
The Spain great posted a tweet of his arrival, saying: "Back to work. Day one."
Porto's players are expected to undergo routine medical tests before the full pre-season training programme gets underway.
Casillas' future remains unclear, although he insisted last month there was no truth to rumours he has already decided to retire and assume a role on Porto's board of directors.