However, the official reason behind Ozil's absence was illness, and Emery insists that reports to the contrary have no truth to them whatsoever.
Emery's men responded well to their latest setback, levelling five minutes later as Monreal was on hand at the back-post to turn home Hector Bellerin's deflected cross.
Team News! Arsenal first!
Arsenal have had a rough start under new coach Unai Emery although much of that is a function of the hard schedule that had them face off against Manchester City and Chelsea in their first two games.
The 29-year-old is Arsenal's highest earner, having been handed a bumper £350,000-a-week deal in January, though has done little to justify that status so far.
Arsenal boss Unai Emery says the emergence of Matteo Guendouzi has been an unexpected bonus in the opening weeks of the new season.
Ozil has blown hot and cold during his time at Arsenal.
An entertaining and error-strewn contest continued to flow from end to end but an injury to Arnautovic robbed West Ham of their prime attacking threat before Diop erred.
Despite the defeat, manager Pellegrini says he was happy with the performance overall.
West Ham United scored the first goal of the match in the 25th minute through Marko Arnautovic after gaining a superb assist from Felipe Anderson.
Benefitting from more astonishingly slack defending, Robert Snodgrass should have put West Ham ahead when he ran clear on goal, but the midfielder let Arsenal off the hook with a tame effort.
The Gunners will hope that they can get off the mark without Özil, with the London side now pointless after losses to Manchester City and Chelsea.
Unai Emery has faced Manuel Pellegrini 10-times before, with the Spaniard winning thrice to the Chilean's four wins.
Another former Arsenal player made an immediate impact as goalkeeper Lukasz Fabianski kept out Henrikh Mkhitaryan's strike with a tremendous stop. Arsenal look much improved when Lacazette is on the pitch.
Fellow forward Alexandre Lacazette, who came on as a substitute against Manchester City and Chelsea, is also yet to score.