Canadian GP: Nico Rosberg thinks Mercedes' pole run under threat

Ferrari's Fernando Alonso set the pace in the fully-dry afternoon session on Friday, with Rosberg fifth fastest.

The German has been on pole position for the last three grands prix, converting that Saturday performance into a race win for the first time this year in Monaco a fortnight ago.

"It looks quite tight out there in general," Rosberg said of the practice timesheets.

"Fortunately I'm feeling good with the car in the rain and the dry. From that point of view it doesn't really matter, but it's still going to be very tough.

"Maybe this track has brought things closer together because it's very different, with lower downforce."

Rosberg's team-mate Lewis Hamilton believes his personal performance will be better in Canada, even though he is still not fully comfortable with the Mercedes. Hamilton was second-fastest in practice.

"If it's dry, I think we are really competitive," he said. "The car feels very good, I feel pretty on it this weekend so it's good.

"I wouldn't say it's a big step forward, I still don't feel right in the car for some reason.

"I don't know if it's my seat, today I was doing my belts up really, really right - which I never do. Maybe I'm moving around in the car too much but it's a little bit better today."

Although Rosberg described tyre degradation as "quite big", Hamilton does not think Mercedes has any concerns on that topic this weekend.

"I don't know what the tyres look like in terms of wear, but they were feeling quite good," he said.

"They told me to push for the last couple of laps, which I was able to do so I had the grip.

"I don't think we're in any trouble at the moment."