However, the formation has worked well for Liverpool, and Rodgers could continue with it even when Johnson returns, putting the England international into a wing-back role.
Allen admitted that he didn't have much experience playing in such a system having missed the last seven weeks through injury, but he is keen to adapt to it as quickly as possible in order to regain a spot in the starting lineup.
"I haven't got great experience of playing it, to be honest, but you can see how well it has worked for the team. We've got the players that can adapt to many different formations, which is a great thing," Allen told the club's official website.
"It's a formation that's working great for us at the moment. There are a couple of slots in midfield, where there is a lot of competition for it; my job now is to work as hard as I can to try to get one."
Liverpool will go into Saturday's match against Newcastle joint-top of the Premier League with 16 points from their opening seven games.