Arsenal captain Martin Odegaard is a doubt for Sunday's North London derby having been pictured using crutches to board a plane to London after injuring his ankle in action for Norway.
A distraught Odegaard needed help leaving the pitch and had to be substituted after turning his ankle during the second half of Norway's Nations League win over Austria in Oslo on Monday night.
Norway head coach Stale Solbakken told broadcaster TV2: "It looked bad in the dressing room too."
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Team doctor Ola Sand initially described the injury as a "small ankle sprain", later adding to Norwegian outlet VG that the midfielder will undergo an MRI scan at Arsenal.
Arsenal plan to assess Odegaard on Tuesday, after he has flown back to London, but he looks doubtful for the game against Tottenham, live on Sky Sports. The photographs of him using crutches, published by VG, raise fears of a lengthy absence.
Riccardo Calafiori also suffered an injury during the international break, hurting his ankle in Italy's Nations League game against France on Friday, but the defender is already back in London and working to be ready for Sunday's game.
Odegaard's injury is a bigger concern and leaves Mikel Arteta facing the possibility of being denied his entire first-choice midfield for the trip to the Tottenham Hotspur Stadium.
New signing Mikel Merino fractured his shoulder in his first training session for the club and is not expected to debut before October, while Declan Rice is suspended due to his peculiar dismissal against Brighton.
Odegaard's injury could not be worse timed. Arsenal start their Champions League campaign at Atalanta on Thursday night before facing a quick turnaround to play at Manchester City on Sunday, live on Sky Sports.
Arteta now faces a dilemma around how to configure his midfield on Sunday. Leandro Trossard could be redeployed, as could Kai Havertz, but the latter option may depend on the availability of Gabriel Jesus, who has not featured since the opening day of the season due to a groin problem.
Raheem Sterling could be drafted in on the left wing for his debut if Trossard is moved. Arsenal's only other experienced options in midfield are Thomas Partey and Jorginho, although Arteta could turn to youth, in Ethan Nwaneri or Myles Lewis-Skelly, or redeploy a defender such as Oleksandr Zinchenko or Jurrien Timber.
'You have to deal with injuries'
Former Arsenal striker Alan Smith to Sky Sports News:
"Martin Odegaard would be a huge loss against Spurs, of course it would, but these things do happen. You've got to cope with it.
"Arsenal were hardly without him last season. More often than not he was there pulling the strings.
"He is such an important player for the team in terms of what he creates. He always wants the ball and can get Arsenal on the front foot really quickly.
"Hopefully the injury is not too bad. You can imagine Mikel Arteta seeing the pictures of him limping off, especially with Declan Rice suspended for the trip to Tottenham as well.
"Two of his three midfielders may not be there for such a huge game, but you have to deal with things like this and that is why every manager wants a big and strong squad. "
Why Arsenal cannot afford to lose Odegaard
Sky Sports' Sam Blitz:
Arsenal have one player in the team they cannot afford to be without and that is captain Martin Odegaard.
The Norwegian midfielder is the heartbeat of the team and his world-class levels both with and without the ball are not only crucial to Mikel Arteta's side, but also impossible to find elsewhere in the team.
Odegaard was the most creative player in the Premier League last season, with the Arsenal captain topping the expected assist tally of 11.17. The only player who got close to that mark was team-mate Bukayo Saka, who got 11.
But it is his role in Arsenal's pressing is where Odegaard is so vital. No player won more possessions in the final third than him last season, while only five players have managed more pressures leading to a turnover than the Gunners midfielder.
More worryingly, Arsenal have a serious midfield crisis going into Sunday's North London derby at Tottenham, live on Sky Sports. Mikel Merino is out for a while with a fractured shoulder, while Declan Rice is suspended for the game after his red card against Brighton.
With Emile Smith Rowe and Fabio Vieira allowed to leave in the transfer window, it leaves Arsenal worryingly short in central midfield. Thomas Partey - not always reliable fitness-wise himself - is now a guaranteed starter. Arteta must pick who out of Jorginho, Kai Havertz and Leandro Trossard could play alongside him in the No 8 role if Odegaard ends up on the absentee list.
The Arsenal manager could also turn to youth, with Ethan Nwaneri and Myles Lewis-Skelly - both yet to make a Premier League start for the Gunners - impressing in pre-season. Ben White, Jurrien Timber and Oleksandr Zinchenko also have midfield experience in their careers and often end up in that area of the pitch as inverted full-backs.
But it is not an ideal situation for Arsenal, who have three busy away trips to Spurs, Atalanta and then Man City in their first seven days after the international break.
They have already dropped points to Brighton this season and may not want any more slip-ups in this unforgiving title race with Man City.
Seven games in 21 days - Arsenal's busy month ahead
September 15: Tottenham (A), Premier League, live on Sky Sports, kick-off 2pm
September 19: Atalanta (A), Champions League, kick-off 8pm
September 22: Man City (A), Premier League, live on Sky Sports, kick-off 4.30pm
September 25: Bolton (H), Carabao Cup third round, live on Sky Sports+, kick-off 7.45pm
September 28: Leicester (H), Premier League, kick-off 3pm
October 1: Paris Saint-Germain (H), Champions League, kick-off 8pm