The Zenit St Petersburg player is reported to have suffered a muscle injury in his left leg.
Hulk stopped training on Sunday morning in Teresópolis mere minutes after starting. He limped off for treatment and did not take any further part in practice.
Brazil coach Luiz Felipe Scolari replaced Hulk with Bernard in the first game against Croatia, making the diminutive winger the most likely contender to face Mexico on Tuesday, if his teammate does not recover in time.
