Diaby had looked back to his best at the start of this campaign and was in splendid form until he was forced off 17 minutes into the France international now faces three weeks on the sidelines with a thigh strain, which has frustrated the Arsenal boss.
Wenger apportioned some of that blame to his handling by the French national team, saying: "I said many times that if France wanted Diaby in Spain (for the World Cup qualifier on October 16) they should not take him for (the qualifiers against) Finland and Belarus."
He went on: "They could have taken him but not played him because the guy has been out for a year, played four or five games.
"You have a breather, give him two weeks to recover completely. I think it was a mistake to play him with the French national team."
Wenger added: "It is as well an opportunity for somebody else to stand up and play but it is a blow, yes.
"Not only because we lost a good player but because he has qualities that the other players haven't got.
"For example, on Saturday when he moved out Alex Oxlade-Chamberlain comes in, takes his position straight away and loses the ball on set-pieces. This is a ball Diaby would have won easily because he has the size.
"We have better balance size-wise and strength as well because he has the power.
"It is really frustrating because once you think you get there it (an injury) happens again."