The Catalans are keen to add a new right-back to their squad as they prepare for life after Dani Alves, who has been linked with a move away from Camp Nou, and they see the 24-year-old Douglas as a good addition to their back-line.
The transfer is not a done deal just yet, but Sao Paulo are confident of reaching an agreement by the end of this week.
"The initial transfer fee will be €6m, but if may rise to €8m if Douglas achieves certain goals which have yet to be defined. Negotiations are nearly done," Sao Paulo vice-president Ataide Gil Guerreiro told Radio Jovem Pan.
"However, certain things may arise that could hold up the deal during contract discussions. We still have some way to go before both sides are speaking the exact same language on a number of details. I think it will be a done deal within three or four days.
"We have asked for Douglas to stay at Sao Paulo on loan for another season, but we are still in talks over this. It is a remote possibility as things stand."
Rumours suggested Dani Alves would join the Brasilerao outfit as part of the deal but Guerreiro insists this is not the case.
"Dani Alves to Sao Paulo? There is nothing to these rumours. He has a high salary and we are not interested in signing him," he added.
Douglas is a product of the Goias youth academy and joined Sao Paulo in February 2012.