Ecuador international Christian Benitez passed away on Monday, aged 27, his club El Jaish have confirmed.
The forward began suffering with severe stomach pain and was rushed to hospital in Qatar but suffered a deadly cardiac arrest.
The striker, nicknamed Chucho, had recently completed a move to the Doha-based outfit from Club America but he has passed away before making his debut.
"The club sends its condolences to Ecuadorean Christian Benitez, a professional footballer who died this morning," El Jaish wrote on their official Twitter account.
The Ecuador FA confirmed the cause of death in an official statement.
"The FEF regrets to inform you of the death of Christian Benitez, the striker of Qatar club Al Jaish and the Ecuador national team.
"Benitez, who was with his new club in Qatar, had a severe stomach pain, which was why he was rushed to a hospital, where after a few hours suffered he suffered a cardiorespiratory arrest, which ended his life.
"The Ecuadorian Football Federation extends its heartfelt sympathy to the family - parents, wife, children - and friends of our striker Christian Benitez.
"May he rest in peace."
Ecuador team-mate Antonio Valencia of Manchester United expressed his condolences having been informed of Benitez's death.
"You'll always be my brother. This pain is hard, my brother, but we love you," the winger, who also played alongside the 27-year-old at El Nacional, posted on Twitter.
Cleber Chala, another former team-mate of Benitez's at El Nacional, tweeted: "You will live in our hearts forever, Chucho."
The ex-Santos Laguna and Birmingham City forward appeared 58 times for Ecuador during his career, scoring 24 goals.