Declan Rice was not present in Arsenal training the day before their Champions League quarter-final with Sporting CP.
Rice's absence from training does not mean he is ruled out of the last-eight clash on Wednesday night, but it is a concern given this is a huge week in Arsenal's season.
With Arsenal needing to finish the job against Sporting CP on Wednesday - Gunners lead 1-0 on aggregate - Arsenal also have a huge Premier League clash with Manchester City on Sunday, live on Sky Sports, which is billed as a 'title decider'.
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Arsenal have been missing Jurrien Timber, Bukayo Saka, Martin Odegaard and Riccardo Calafiori in recent weeks - and none of them were in open training on Tuesday morning.
Piero Hincapie and Eberechi Eze - who were only fit enough for the bench for the defeat against Bournemouth on Saturday - were both in training.
Mikel Arteta will give more information about Rice's absence from training - and the rest of Arsenal's injury news - in his press conference at 1.30pm.
Who could replace Rice?
Sky Sports' Sam Blitz:
It's the last bit of news Arsenal wanted to hear - more injury woes. But this may be the most agonising injury concern of the lot.
Not only is Declan Rice one of Arsenal's best players - an irreplaceable cog in Mikel Arteta's system - but there is also no back-up option for him. That's because Mikel Merino, Rice's back-up in his midfield position, is also sidelined with a long-term injury.
So where do Arsenal go from here if Rice is missing from their Champions League quarter-final second leg?
Christian Norgaard is Arsenal's only other available option as a sitting midfielder, but he is deemed as a back-up to Martin Zubimendi, rather than for the more attacking Rice.
Kai Havertz could continue in midfield, alongside Zubimendi and Eberechi Eze - but that is a very attacking set-up - and could expose Zubimendi, who is out of confidence at the moment.
There are other options. Leandro Trossard has shown he could play in midfield - and even started last season's Premier League game away at the Etihad Stadium, though was sent off before half-time. Myles Lewis-Skelly is another player who could fill Rice's role.
Either way, it is not ideal preparation in what is a big week not just in Arsenal's season - but also Mikel Arteta's tenure at the club.
Arsenal's remaining fixtures
April 15: Sporting CP (H), Champions League quarter-final second leg, kick-off 8pm
April 19: Man City (A), Premier League, live on Sky Sports, kick-off 4.30pm
April 25: Newcastle (H), Premier League, live on Sky Sports, kick-off 5.30pm
April 29: Barcelona/Atletico Madrid (A), potential Champions League semi-final first leg, kick-off 8pm
May 2: Fulham (H), Premier League, live on Sky Sports, kick-off 5.30pm
May 5: Barcelona/Atletico Madrid (H), potential Champions League semi-final second leg, kick-off 8pm
May 10: West Ham (A), Premier League, live on Sky Sports, kick-off 4.30pm
May 17: Burnley (H), Premier League, kick-off TBC
May 24: Crystal Palace (A), Premier League, kick-off 4pm
