Panathinaikos and Greece international George Baldock was found dead in his swimming pool on Wednesday, Greek news reports said.
The 31-year-old English-born right-back died at home in the southern Athens suburb of Glyfada, state agency ANA said.
Greece’s Super League and several clubs expressed their condolences.
State TV ERT said the player was “at the bottom of the pool” and a bottle of alcohol was found at the scene.
ANA said Baldock’s wife, who is abroad, alerted the owner of the residence after unsuccessfully trying to reach the player on the phone.
Police cars and an ambulance were outside the building and a coroner was called to examine the body, ERT said.
Baldock had joined Panathinaikos in May after a seven-year spell with Sheffield United, relegated from the English Premier League to the Championship last season.
Of Greek origin through his father, he was called to the Greek national team in 2022.
He had 12 caps, but had not been selected for the team’s Nations League match against England at Wembley on Thursday owing to injury, ERT said.
Baldock had featured for Panathinaikos in a 0-0 draw with Olympiacos in a Greek Super League match on Sunday where he played for 75 minutes.
Both the Greece team’s official website and his club’s social media sites on X, formerly Twitter, and Facebook, were blackened in tribute to the player.
Manchester United’s England international defender Harry Maguire, a former Sheffield United player, posted “RIP” and a heartbreak emoji alongside an image of Baldock on Instagram.
Sheffield United changed their home page to a black and white photo of their former player with the words: “RIP George Baldock.
“Sheffield United Football Club is shocked and extremely saddened to learn of the passing of former player, George Baldock,” said the club.
Northampton, where Baldock had a loan spell in 2011, wrote on X: “We are deeply saddened to learn of the passing of former loanee George Baldock at the tragically young age of 31.
“George made five appearances in 2011 before playing for Oxford United and Sheffield United. Sending our sincerest condolences to George’s family and friends.”