'Night and day' Mercedes Monaco GP slump puzzles Lewis Hamilton

Hamilton topped the times in the morning session, but in the second session could not better eighth, while team-mate Valtteri Bottas was 10th.

Both men were over 1.1 seconds off the pacesetting Ferrari of Sebastian Vettel as they struggled for grip in the hotter conditions.

Asked if he could explain Mercedes' results, Hamilton replied: "I can't, because I don't understand it.

"P1 was really good, the car was feeling great.

"Then there was night and day difference, black and white.

"P2 was a little bit different, we couldn't work the tyres for some reason, lots of sliding about.

"A lot of studying to do to find out where we went wrong, but I'm confident in my guys.

"I don't know if it's set-up. It's just with the tyres, I don't know why the tyres weren't working."

Hamilton was relieved that Mercedes can use the Friday rest day to try to address the problem before track action resumes on Saturday.

"That's something we have to study and figure out for Saturday," he said.

"It gives the guys here more time to work on the car, spread over two days, rather than everything tonight."

Mercedes technical director James Allison suggested an errant set-up direction was to blame.

"After a very positive morning session with both cars and drivers, the afternoon proved more difficult and we clearly took a step in the wrong direction with the car set-up over the break," he said.

"We will have a good think about it tomorrow in order to put things right for Saturday."