The powerful 26-year-old midfielder has been in fine form for Arsenal this season after a lengthy absence, but his latest injury leaves him on the sidelines for at least three weeks.
And Wenger feels if Diaby remained fit and firing against Roberto Di Matteo's side, then his team could well have gone on to win the match.
"Losing Diaby is a blow, yes. Not only because we lost a good player but because he has qualities that the other players haven't got," he told reporters.
"For example, on Saturday when he went off, Alex Oxlade-Chamberlain came on, took his position straight away and we lost the ball for a set-piece.
"It was a ball Diaby would have won easily because he has the size. We have better balance with him because he has the power.
"It is really frustrating because once you think you get there it happens again."
Despite the injury to his strong central midfielder, Wenger called on the rest of his midfielders to fill the void left by Diaby.
He added: "We have Aaron Ramsey, Francis Coquelin, Alex Oxlade-Chamberlain and Jack Wilshere. It depends on if you want to be more offensive.
"Arteta can play higher and deeper, as well. So we can put a deeper midfielder in like Coquelin and then Arteta can move forward."
Unfortunately for Arsenal, Arteta may also be missing for the Wednesday night Champions League clash with Olympiakos after suffering an ankle problem, and the Spaniard will have an early fitness test.
But Wenger is refusing to rush England midfielder Wilshere back into action after the youngster started his comeback in the Arsenal Under-21 side on Monday against West Brom after 14 months out with ankle problems.
Wenger stated: "[Wilshere] came through it OK. It is now down to taking the right time to get him slowly back."
And despite the loss to their London rivals, Wenger insisted his side can rectify their poor defending from set pieces and succeed this season in both domestic and European competition.
He continued: "There were a lot of positives in [against Chelsea] as well, what was not good is easy to correct. I believe the championship is long, but we have to make sure the Champions League is long as well."