Teixeira had been playing for Moldovan club Sheriff, but hadn't featured for them since the final day of last season.
The centre-back joined Stoke for a reported £400,000 from Dukla Banska Bystrica in 2013, but only made two Premier League substitute appearances for the Potters, against Aston Villa and Bournemouth.
He also had a loan spell at Fleetwood Town in 2015/16, where he played 10 times.
Sheriff said in their official club statement: "A few hours ago, a good man and an excellent football player, former FC Sheriff player Dionatan Teixeira, died.
"The Brazilian defender was only 25 years old. The whole of the club is shocked by this tragic news. The pain of loss is great.
"We express our sincere condolences to the relatives and friends of Dionatan."
Former club Stoke tweeted: "The thoughts of all at #SCFC are with the family & friends of our former player Dionatan Teixeira following his untimely passing, aged 25."
