Arsene Wenger has stated that Arsenal will use both a back three and a back four at times this season.
The Gunners have deployed a formation with three central defenders since April, with the new system helping them win the FA Cup.
But they have looked far less convincing with three at the back in recent weeks, particularly in games against Leicester and Liverpool.
Arsenal started their Europa League opener against Cologne with a three-man central defence on Thursday, and they struggled at times.
But after Wenger brought on Sead Kolasinac and changed the formation to a four-man defence, they fared much better and recovered to win 3-1.
We expected that it would be the end of the experiment, but Wenger suggested otherwise on Thursday.
“I want to use both systems when it suits the team or when we need to do it,” he said.
“Because we played for a long time in a back four, it is easy for me to switch from a back three to a back four.”