Jenkinson played the first hour of the Gunners' 2-1 defeat to Tottenham Hotspur in the North London derby on Sunday afternoon, before being replaced by Tomas Rosicky.
The result leaves Arsene Wenger's side five points adrift of fourth-placed Chelsea with 10 Premier League games left to play. Jenkinson believes that Arsenal have not performed to their best on a consistent basis this season.
"On our day we can beat anyone," Jenkinson told Arsenal's official website.
"I genuinely believe that. When we play to our potential, teams can't come near us, but we need to do that consistently. If we do that we will be fine, but we just can't find the consistency at the moment.
"We played well [against Tottenham] in patches, but then we'll have 10 minutes where we'll drift out of the game a little bit."
Arsenal are next in action when they host Everton on Saturday.