Arsenal will not have Gabriel for their Champions League quarter-final tie against Real Madrid after he was ruled out for the rest of the season.
The centre-back, who has been one of Arsenal's most key players this season, suffered a hamstring injury in the first half of Tuesday's Premier League win over Fulham, which will require surgery.
Arsenal have said the 27-year-old's aim is "to be ready for the start of next season."
Mikel Arteta's side take on Real Madrid in the first leg of their Champions League quarter-final tie at the Emirates on April 8, before the return leg at the Santiago Bernabeu on April 16.
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Arsenal, Fulham
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Arsenal were boosted by the return of Bukayo Saka against Fulham, but they are facing a potential injury crisis in defence ahead of next week's first leg against Real Madrid.
Jurrien Timber was also hurt during Tuesday's game while Ben White and Riccardo Calafiori were already sidelined alongside season-long absentee Takehiro Tomiyasu.
Kai Havertz and Gabriel Jesus, Arsenal's first-choice striker options, are out for the season too.
Analysis: Gabriel injury a nightmare for Arteta
Sky Sports' Nick Wright:
Gabriel's despondent demeanour as he made his way off the pitch against Fulham told a tale. He knew it was a serious injury and so it has proved. Arsenal's hamstring curse continues.
He is their third player to have required surgery after tearing the muscle this term, after Bukayo Saka, who has only just returned from a three-month absence, and Kai Havertz, who is out for the season too.
Gabriel's injury is every bit as big a blow as those losses. The Brazil international is vital to Arteta, his centre-back partnership with William Saliba is statistically the best in the Premier League.
Gabriel has mostly been reliable in terms of his availability during his time at Arsenal but the side's record with and without him starting underlines his importance.
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The timing of his injury is a nightmare for Arteta with Real Madrid around the corner and defenders already missing.
Jurrien Timber was also forced off against Fulham following a knock to his knee, while Ben White missed the game against Fulham with a niggle and Riccardo Calafiori is facing weeks out with a knee injury. Takehiro Tomiyasu's long-term absence means they are down five defenders in total.
Gabriel is by far the most important of them. An outstanding defender and a deadly goal threat at set-pieces, the 27-year-old has also become a leader too. His warrior mentality, in addition to his many other qualities, will be a huge loss in the battle that lies ahead against Real Madrid.