Arsenal are sweating on the fate of Gabriel Jesus after the striker returned to London for further tests on the knee ligament injury that ended his World Cup.
The 25-year-old was hurt during Brazil's defeat by Cameroon last week and has been seeing a specialist after returning from Qatar.
It's understood Arsenal are hopeful the damage is not too serious, with Brazil initially indicating Jesus could face three months out.
Further assessments on Tuesday should give Arsenal a clearer picture of whether the striker needs surgery.
Until then, club sources insist, it is difficult to know definitive timelines - or whether Arsenal will need to look for a replacement in the January transfer window.
Manager Mikel Arteta has been in the United States alongside sporting director Edu and owner Stan Kroenke.
Arteta and Edu have been in contact with Jesus but on Monday flew to Dubai, where Arsenal will play matches against Lyon and AC Milan.
Arsenal's head doctor Gary O'Driscoll has stayed in London to work with Jesus.
The £45million summer signing has been fundamental to Arsenal's fine season, helping Arteta's side secure a five-point lead over Manchester City at the top of the Premier League table.
Jesus has started all 14 of their league fixtures, amassing five goals and six assists and dragging Arteta's attack to new heights.
Without him, Eddie Nketiah is the only recognised No 9 in Arsenal's squad and a long-term injury could force Arsenal to rethink their plans for the January window.
The north London side had been focused on adding a winger, and possibly a central midfielder, to their squad.
They face big games against Manchester United and Tottenham in the first few weeks after the World Cup.