McLaren drivers Jenson Button and Lewis Hamilton admit they have some concerns about Lotus' pace in Monaco despite Button finishing quickest.
Romain Grosjean proved to be the most consistent driver around the streets of Monte Carlo on Thursday, finding pace in both practice sessions.
The Frenchman finished second in FP1, three-tenths down on Fernando Alonso, and repeated that feat in the day's second session, this time three-tenths down on Button.
This prompted Button to declare that Lotus will be the favourites to dominant the Monaco Grand Prix weekend.
"The cars that looked very fast for me were the Lotus," said the McLaren driver.
"Their runs whenever they are out look very competitive, so I'd say the Lotus is the car to beat so far this weekend."
Button, though, was the one to be beat in FP2 as, in the minutes before the rain, the Brit ventured out on the super soft tyres to post a 1:15.746 - the fastest time of the day.
"From P1 to P2 the car has improved, as there was something that I didn't like in P1, so we've tried something different and it's worked," he said.
"So I'm happy with the way the car feels, but we are still not there yet. We were quickest, but we were one of the only cars to do a timed lap on the super soft.
"I don't think it's massively quick, but the car feels okay and I think there's a lot of room for improvement. We know the direction that we can take."
As for his team-mate Lewis Hamilton, the Brit echoed Button's sentiments about Lotus but added that the team who are third in the Constructors' Championship won't be McLaren's only obstacle.
"The Lotus is massively quick," Hamilton told Autosport.
"I'm not really quite sure what Red Bull is up to, but I have no doubts they'll be quick. The Ferrari is very quick.
"The same teams are quick this weekend. I think everyone's got the chance to fight for the front end.
"It's all about making sure you get out there at the right time, you get the temperature into your tyres and your brakes, and you nail it on the lap that you get."