Elneny scored one of the goals that condemned Olympiacos to defeat after he was afforded his seventh appearance in the European tournament this season.
The game started brightly with Arsenal dominating the opening 30 minutes and came close to opening the scoring in the seventh minute, when Gabon international Pierre-Emerick Aubameyang’s header hit the crossbar.
The moment eventually came for the Gunners to break the deadlock in the 34th minute when Martin Oedegaard fired a long-range shot home from outside the box.
After the restart, the Greek champions made a frantic effort to level proceedings and got an equaliser through El-Arabi in the 58th minute.