Ferrari's Felipe Massa thinks that overhauling Mercedes will be a difficult proposition in qualifying, but believes they will be able to fight with them.
Nico Rosberg set the quickest time in both practice sessions in Monaco.
"The weekend has got off on the right foot, the car behaved well and I managed to find a good pace," said the Brazilian.
"I finished in the top five in both sessions, which is important in such an unpredictable event as the Monaco Grand Prix. However, we are aware that we still have much work to do."
"Now we will analyse all the data available to try and find the right direction to go in, because here it’s vital to have a car that is both competitive in qualifying and performs consistently in the race. Mercedes has shown that it is quicker and it will not be easy to get ahead of them in qualifying, but I am sure we have what’s needed to take the fight to them."
Team-mate Fernando Alonso was third quickest and is upbeat about the remainder of the weekend.
"Even if the feelings are positive and we got through the day without any problems whatsoever, we still don’t have a clear idea of the pecking order in the field," he said.
"We will have to wait a bit to see where all our rivals really are, because here too, until Saturday, no one pushes a hundred percent: the barriers constitute too high a threat to take risks in the first free practice sessions. There’s not much time to do a tyre comparison here, we did only one and the results didn’t throw up any surprises: the Super Softs are a bit quicker and degrade more."