The 27-year-old was forced to stop after only 10 minutes of Sunday's training session, leaving him as a concern for the Selecao's next match following an opening winHulk limped out of Brazil training on Sunday morning, leaving the striker as a doubt for the World Cup hosts' second match of the competition against Mexico on Tuesday.
The Zenit St Petersburg forward started as the Selecao kicked off the competition with a 3-1 victory over Croatia, though he was forced to leave his team-mates prematurely as they continued their build up for the North Americans, whom they will meet at Fortaleza's Stadio Castelao.
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"I'm fine, I'm cool," he told the press. "I prefered to exercise caution, as there is only two days before the game.
"I'll travel with the squad but it's Scolari who will decide at the last minute. If I play it's because I can give my best."
Although team doctors have not yet commented on the severity of the problem, there is a chance that the forward could miss the Mexico clash.
His absence would force coach Luis Felipe Scolari to change the dynamic of the side, with some suggestions that Ramires could be drafted in as an additional body in the midfield, though Bernard, who replaced the 27-year-old midway through the second half of the opening game, and Willian would represent more attack-minded alternatives.
Hulk has won 36 caps in total for his country and scored nine goals, often playing out on the right wing, which allows him to cut inside and shoot off his stronger left foot.