Paul Walsh said it was difficult to gauge how good Manchester City were in their one-sided 5-0 victory over Steaua Bucharest in the Champions League qualifier.
City created a string of chances and could have won by a greater margin, with Sergio Aguero missing two penalties before scoring a hat-trick.
Steaua did not help their cause with some slack defending against Pep Guardiola's side, who capitalised on their superiority with some ruthless finishing.
Asked on Soccer Special whether the team are starting to understand Guardiola's plans, former City forward Walsh said: "It's hard to tell when you are up against poor opposition because you don't get tested.
"It was a training session. It could have been nine, easily. Defensively they never really got tested. John Stones looked comfortable but against Bayern Munich will he be like that?
"That's when the pressure is really on. You want them to be more effective in the big games in Europe and the Premier League."
City have one foot in the group stage of the competition before the second leg at the Etihad next Wednesday.
And Walsh added: "City were so much the better team, (Raheem) Sterling was really lively, Nolito showed flashes of quality and (Pablo) Zabaleta had a good game.
"Guardiola is trying to find out where everybody is the most effective."