The France international is expected to be out of action for around a month.
The Gunners are not expecting to be in a position to call upon the 28-year-old frontman until into October. As a result, he will definitely sit out a trip to Watford on Sunday.
Arsenal have further Premier League games against Aston Villa, Manchester United and Bournemouth to come before the next international break.
Unai Emery’s side will also take on Eintracht Frankfurt and Standard Liege in the Europa League, while facing Nottingham Forest in the Carabao Cup.
It remains to be seen how many of those fixtures will see Lacazette reduced to watching a brief, with Arsenal stating in a fitness update on their official website: “After assessments to an ongoing ankle issue, we have advised that Alex will need to rest and strengthen his ankle to regain full fitness.
“Alex has been playing through this injury for several weeks. He is likely to be back in action in October.”
While Lacazette is now out of action, a number of players who have been nursing knocks over recent weeks have returned to training.
Among those to have been welcomed into Emery’s plans are Hector Bellerin and summer signing Kieran Tierney, although neither full-back is ready for selection just yet.
Emery said at a pre-match press conference: “We need to look at the next steps in each training and also if we decide to play with Under-23s, maybe they can take confidence, better rhythm and then be ready to play with us at 100 per cent.
“They did this week the first time training normally with us. We want the next week to take the normality training with us.
“After that week we can decide how they are to start playing with the under-23s and us [the first team].”
Tierney and Bellerin will not be in contention to face Watford, with Emery looking to piece together an XI to take on a Hornets side that is now back under the guidance of Quique Sanchez Flores.
“They finished with Javi Gracia and did a very great season last year. Now they’ve signed a very great coach also with Quique Sanchez Flores,” Emery said.
“We [Emery and his staff] played against him in Spain, his teams are very organised. He has a good experience here in England and the Premier League with Watford. I respect him a lot.
“He is going to know the team and players. He knows some players because he trained there three years ago. He’s going to do well.
“I really respect every coach. I think now with Sanchez Flores they will continue working well like they were doing with Javi Gracia.
“We are going to respect them, prepare the match thinking about us and after respecting their characteristics.
“Their characteristics are going to be the same. They are going to push a lot with their supporters, they have very good players.”
- Pierre-Emerick Aubameyang indicates he’s unhappy with Unai Emery’s tactics after Watford
- Ozil out, Aubameyang out: Arsenal’s probable XI vs Napoli
- Some Arsenal players ‘confused’ by Unai Emery’s recent tactics
- Arsenal Beat Watford to go 4th in the Premier League Table
- Unai Emery gives injury update on Xhaka & Koscielny ahead of Napoli