The bus was heading from the southern city of Cuenca to the coastal city of Guayaquil, where Barcelona is based, after a local tournament game.
The vehicle apparently ran off the road and flipped around 2130 GMT, Ecuador’s Transit Commission (CTE) said in a statement.
The president of Barcelona Sporting Club, former national goalkeeper and World Cup veteran Jose Francisco Cevallos, published the death toll on Twitter.
“We received the news of the accident of our fans… with much pain,” wrote Cevallos, who is also the governor of Guayas province where Guayaquil is located.
“We are making arrangements to quickly get the bodies to give them a Christian burial,” added Cevallos, who is also a former sports minister.
Transit authorities had initially said that 10 people had died and 35 were injured in the accident.
Cevallos later told reporters that a wake would be held for the victims at the football club’s home stadium in Guayaquil.
A firefighter at the scene of the accident, citing a witness, told Teleamazonas TV that the bus driver had tried to cut off another vehicle just before the accident.
In Sunday’s game Barcelona tied 1-1 with Deportivo Cuenca. The rival team offered their condolences and “solidarity” via Twitter, and offered wishes for the “quick recovery” of those injured.
Officials said the bus had passed its most recent safety inspection.
Traffic accidents are among the leading causes of death in Ecuador. According to the watchdog group Justicia Vial, on average seven people are killed and some 80 people injured each day in traffic accidents.
And 96 percent of those accidents are due to human error, usually the driver’s fault, according to the group’s figures.