Per Mertesacker will miss the start of the season with a potentially serious knee injury that ruled him out of the pre-season trip to the United States.
While the extent of that injury is not yet fully known it is likelier to keep him out for months rather than weeks.
The problem for Arsenal is that their other experienced centre-back Laurent Koscielny will also miss the start of the season.
He is not expected back from pre-season training until Monday 8 August, having been given four weeks to recover from Euro 2016.
Koscielny and Olivier Giroud both played for France in the final, which they lost to Portugal on 10 July, and Arsene Wenger has promised that he will not rush the pair back into first team action.
That means that Giroud and Koscielny are unlikely to be ready for the Liverpool game at the Emirates on 14 August.
They are likelier to return against Premier League champions Leicester City on 20 August or even against Watford on 27 August.
Mesut Ozil and Aaron Ramsey, who return to training this Monday, will be racing against time to be ready for the Liverpool game too.
This leaves Arsenal short of both of their leading centre-backs for the start of the season.
Gabriel, signed from Villarreal in January, is almost certain to start against Liverpool and Leicester City, providing he can recover from an injury that kept him off the trip to the US.
But Gabriel will have to be partnered either by a young player or a part-time centre-back.
Calum Chambers is the likeliest solution but Arsene Wenger lost faith in him last season and he only started two Premier League games, having started 17 in the league the previous season.
Arsenal have been considering loaning Chambers out but only if they can be confident he will play enough games to develop as a player, and that is far from certain.
Rob Holding, signed this week from Bolton Wanderers, could make the step up to Premier League football after a good season in the Championship last year, which prompted Arsenal to spend £2.5million on him.
EmoticonEmoticon