Arsenal’s Gabriel Magalhães faces a month on the sidelines

Arsenal fear that Gabriel Magalhães could be out of action for at least a month after he sustained a thigh injury on international duty last week, with the Brazil defender expected to miss a crucial part of the season for the Premier League leaders.

Gabriel limped off during Brazil’s 2-0 win against Senegal in a friendly at the Emirates Stadium on Saturday and returned to the club for more tests this week after it was confirmed he had sustained a muscle injury in his right thigh.

The tests are understood to be continuing and Arsenal have yet to confirm how long the influential 27-year-old will be absent, although he is not expected to be available for the north London derby against Tottenham on Sunday or the Champions League meeting with Bayern Munich three days later.

There are concerns that Gabriel could miss at least a month or possibly longer, depending on the severity of the injury. That would also rule him out of Premier League fixtures against Chelsea and Brentford at home and Aston Villa away, as well as the Champions League match at Club Brugge on 10 December. Mikel Arteta’s side – who have a four-point lead over Manchester City – then face Wolves at home before their rearranged trip to Everton on 20 December.

It would be a significant blow to Arsenal’s title challenge to lose a player who has played every minute of the Premier League campaign, especially given Gabriel’s importance to a defence that has conceded just five goals in 11 games and had kept eight consecutive clean sheets in all competitions before the 2-2 draw at Sunderland.

Cristhian Mosquera and his fellow new signing Piero Hincapié are in the frame to replace Gabriel against Spurs. There are also concerns about whether Viktor Gyökeres will be back to lead the line, after the £64m striker missed Arsenal’s final two matches before the international break because of a hamstring injury.

The Germany manager, Julian Nagelsmann, revealed on Tuesday that Kai Havertz has experienced what he described as a “minor relapse” during his recovery from a knee injury after Arteta had been hopeful that the striker could return this weekend. “But overall, he’s doing well,” Nagelsmann said. “He is expected to return towards the end of the year.”

Arsenal’s pursuit of Liverpool last season was undermined by a succession of injuries and they spent more than £250m on reinforcements in the summer. But with Martin Ødegaard, their captain, also on the absentee list along with Noni Madueke and Gabriel Martinelli, their squad is being stretched to the limit.