Wenger faces tough decisions ahead of opening game
The Belgian centre-back was Arsene Wenger's only summer signing and has recovered from a groin problem.
With Kolo Toure having been sold to Manchester City and Johan Djourou (knee) set for a spell out, the 23-year-old is expected to partner veteran William Gallas in a defence which was all too often brutally exposed last season.
Walcott, meanwhile, needs some more time to recover from a slight back problem which kept him on the bench during England's 2-2 draw in Holland.
"We have some problems,'' Wenger said when assessing his squad on their return from the midweek internationals. "We have Theo Walcott, who is not available. Diaby has a little groin problem, but he could be available.
"[Also] we have lost Johan Djourou and Lukasz Fabianski because they had injuries. Lukasz had a cartilage surgery. He will be out for two months.
"Johan has a knee problem that will take some time to cure - one month. Thomas Vermaelen played 45 minutes for Belgium on Wednesday night and came through okay so he will be available.''
At just shy of 6ft, critics have suggested the addition of Vermaelen still leaves the Gunners once again lacking height in a crucial area.
However, the former Ajax defender insists there is much more to his game than just sheer physical presence.
"I am not so tall, I know that, so you have to be good at reading the game,'' Vermaelen said. "I think my heading game is good, I have a good jump and that is positive if you are a centre-back.
"On the field it is just very important to be smart and thinking all the time.''
Vermaelen had been at Ajax since he was 15, and went on to make more than 140 first-team appearance, captaining the side last season as well as playing in the Champions League - which included two appearances against the Gunners in the 2005/06 group stages.
"I will always give 100%,'' he said. "I have a good mentality. I want to do my best for Arsenal, playing as well as I possibly can.
"I think I am decent in the air and technically, and I always want to battle on the pitch.''
While they will miss the Champions League qualifier against Celtic, Wenger is happy with their progress.
"Tomas Rosicky is two weeks away,'' said the Arsenal boss. "Samir Nasri [is out] three-and-a-half weeks now, but it will be six or seven weeks until he is available for training.''