Fernando Alonso says Ferrari "might have to improvise when it comes to strategy" such is the advantage with the Supersoft Pirelli tyres.
The double World Champion concluded Thursday afternoon's practices on the street circuit at the top of the timesheets.
Aided partly by the rain limiting the action, Alonso posted a 1:18.482 as the chequered flag fell to beat Lewis Hamilton by 0.419s.
Although it was an encouraging sign from Ferrari, there have been times this season when they have shown pace in practice only to fall away on the Saturday.
Throw in the time difference between the two Pirelli compounds and Alonso Ferrari may have to adopt a different approach as the Monaco weekend progresses.
"Here in Monaco, the most important thing in practice is to do as many laps as possible, because it is a very special track and you need to have a good feeling from the car," he explained.
"Despite the rain reducing the amount of track time in the second session, we more or less managed to complete all our programme and, with or without a turbo, the complexity of this track remains the same, so doing well in qualifying will be crucial.
"The increase in grip we found over the few laps we did with the Supersoft tyres leaves us in no doubt that this will be the tyre to use on Saturday afternoon, while for the race there is still a lot to learn as no one has done a long run. So we might have to improvise when it comes to strategy."