On Friday, the Brazilian football association (CBF) confirmed both Neymar and Danilo, the right-back who also injured his ankle in the same game, would miss Brazil's next match against Switzerland on Monday.
But sources have told ESPN the pair could also miss their last group game against Cameroon next Friday.
"Neymar and Danilo started treatment yesterday immediately after the game," Brazil doctor Rodrigo Lasmar said in a video published on Friday. "This morning they were reevaluated.
"The tests showed a lateral ligament injury on Neymar's right ankle, along with a small bone edema and a medial ligament injury on Danilo's left ankle. The players are still undergoing treatment.
"We can already say that we will not have the two players for the next game but they remain in treatment with our goal of trying to get them back in time for this competition."
"Nothing in my life was given or easy, I always had to run after my dreams and my goals," he wrote on Instagram. "Never wishing bad for someone but helping those who need something.
"Today became one of the most difficult moments of my career... and again in a World Cup. Yes, I have an injury, it's boring, it will hurt but I'm sure I will have the chance to return because I will do everything possible to help my country, my teammates and myself."
Neymar has scored 75 times in 122 games for Brazil and is now just two goals away from breaking Pele's scoring record for the men's national team.
Richarlison scored two goals to lead Brazil to victory against Serbia at Lusail Stadium as they aim for a record-extending sixth World Cup title.
Danilo, who started as a right-back for Brazil against Serbia, posted a message on Instagram saying he already started his road back to playing again in Qatar.
"If necessary, I will do 25 hours of treatment to recover in time to play even if it's only for a minute. In the meantime, my energy is with my teammates in every situation of the game", Danilo wrote. "My return is already closer! Thanks for all the messages."
Brazil leads Group G along with Switzerland, which opened with a win against Cameroon.