The Gunners are already without the services of Petr Cech who has been sidelined with a thigh injury he picked up during Arsenal's 3-1 defeat to West Bromwich Albion before the last international break. The ex-Chelsea star was replaced by the Colombian international at the Hawthorns and he was in between the posts against Manchester City on 2 April.
Ospina sustained a muscle injury in Arsenal's 2-2 draw against Pep Guardiola's side, which also saw Laurent Koscielny suffer an an Achilles injury. With Cech already on the sidelines, Ospina has joined the Czech Republic player at Arsenal's treatment room and lack of options forced Wenger to field Emiliano Martinez against the Hammers.
"Ospina is out with a muscle injury he got against Manchester City. Petr Cech is not back so Martinez starts in goal tonight. Of course [I have confidence in him]. Every time he has come in he has done well so lets hope that continues. I'm confident," Wenger explained, as quoted by the Express.
The Arsenal manager has refused to state whether either of his two first choice goalkeepers will be fit to face Middlesbrough when Arsenal travel to the Riverside Stadium on 8 April.
Ospina and Cech now join Koscielny in the list of injured players at Arsenal, along with Lucas Perez and Santi Cazorla. The Spain international midfielder went under the knife in December for an Achillies problem and Wenger confirmed that the former Malaga man would be out for the rest of the season.
Meanwhile, Emiliano Martinez has expressed his delight after Wenger handed him his first league start of the campaign against West Ham. The 24-year-old, who was handed a new long-term contract in November, was successful in keeping a clean sheet at the Emirates on Wednesday.
"When they told me I was playing two days ago, all the hard work, all the extra hours in training that I put into the pitch - that's what I did today. I felt comfortable, we played brilliant football and obviously I'm delighted for the win and for the clean sheet as well," Martinez told Arsenal Player.