Shkodran Mustafi has suggested that Arsenal required time to adjust to a new formation during the 1-1 draw with Vitoria de Guimaraes.
While the Gunners had hoped to register their fourth successive win in the Europa League, they had to make do with a share of the spoils courtesy of a last-gasp equaliser from the hosts.
Arsenal produced a disappointing performance in Portugal, although Mustafi has hinted that the decision of under-pressure manager Unai Emery to play with a back three contributed to the result.
The German told BT Sport: "We played with a back three, a system for a long time we didn't play. So we needed our time a little bit to get the rhythm in.
"In the first half we didn't do as we wanted. I think we came out better in the second half, had better rhythm, better passing.
"We need to stay calm. Everyone wants to show and give everything, sometimes when you are over-motivated it's difficult to deal with that."
Each of Mustafi's six appearances this season have come in cup competitions.
Darren Plant
