Arsenal striker Alexandre Lacazette will be sidelined until October with an ankle injury.
The 28-year-old had been playing through the pain, but has now been told to rest the problem.
An Arsenal statement said: "After assessments to an ongoing ankle issue, we have advised that Alex will need to rest and strengthen his ankle.
"He is likely to be back in action in October."
Lacazette has scored two goals in three appearances this season, the last of which came in the 2-2 draw with Tottenham, when the Frenchman was replaced in the 67th minute.
Unai Emery insists Arsenal's club-record signing Nicolas Pepe is ready to face Watford on Sunday after confusion over his fitness during the international break.
The 23-year-old played in the 2-2 draw against Tottenham before the Ivory Coast FA reported he had contacted them to say he had suffered an injury.
That claim was refuted by the Gunners and it was claimed he was purely working on building up his fitness.
Asked if Pepe was fit, Emery replied: "Yes, yes, he is training well and he is ready for Sunday."
While Pepe is fit to play, fellow summer recruit Kieran Tierney is still not yet ready to make his debut.
The Scotland full-back joined from Celtic but has been sidelined by a groin problem - although he has stepped up his recovery in recent weeks.
Both he and Hector Bellerin will not be fit to make the short trip to Vicarage Road but Emery said there is a plan in place to ease the pair back into first-team action.
"Maybe if they play with the under-23s they can take confidence and better their rhythm and then after play with us 100 per cent." he said.