Arsenal centre-back Gabriel Magalhães will be sidelined for at least a month, sources told ESPN on Wednesday.
The Brazil international pulled a muscle in his thigh in the second half of his country's friendly with Senegal on Saturday.
His injury is still being assessed by the Gunners' medical staff but the first diagnosis is a four-week absence. It could be longer too if the injury doesn't scar as quickly as anticipated.
It is a massive blow for Mikel Arteta and his team as Gabriel, 27, has been exceptional defensively and offensively so far this season, starting every Premier League and Champions League match so far.
Arsenal have kept the most clean sheets so far this season in the Premier League (seven and 11 games) and have the best defence too with five goals conceded in 11 games which Gabriel played a big role in. He has also scored two goals already and provided three assists so far in all competitions.
He will miss important games like the North London derby against Tottenham on Sunday, the top of the table clash in the Champions League against Bayern Munich on Wednesday and the trip to Stamford Bridge to face Chelsea next weekend.
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Arteta has various options to replace him at the back, like Piero Hincapié, left-footed like Gabriel, or Cristhian Mosquera.
However, Italy confirmed that Riccardo Calafiori left their camp due to injury.
"He could have played perhaps, but it wouldn't have been fair to him or Arsenal," Italy coach Gennaro Gattuso said.