Red Bull's clean sweep of grand prix wins in 2023 could come to a halt this weekend in Monaco.

The team knew that the particular strengths of the car - top speed and fast corners - would not be exercised on the tight Monte Carlo streets.

"Max was super happy after the simulator runs at the beginning of the week," Dr Helmut Marko said after the two practice sessions on Friday.

"Unfortunately, reality caught up with us. Unfortunately it's not always like the data world."

Indeed, Max Verstappen and Sergio Perez struggled in the first session but had caught up by the next practice outing - even if the gaps to the opponents were very small.

"I wasn't really happy driving the car over the curbs and the bumps," world champion Verstappen admitted. "I think the second practice was already a lot better."

However, he's worried about his competitors this weekend.

"Especially compared to Ferrari, I think we're still a little bit short in terms of the overall performance of the car, how it handles the curbs, the bumps and the corners," said the Dutchman.

Team official Marko agrees: "We have to watch out for (Charles) Leclerc. Maybe also Alonso as well. He drove his fastest lap with a set of tyres that had already done 8 laps.

"Everything depends on the grid position and the start. We can't do anything with our long run pace," the Austrian added.

As for Mercedes, the Brackley based team is happy with its radically-revised 'B' car so far - but the real aerodynamic effect won't be felt until the much more normal Barcelona circuit.

"We are looking good, even if the gap on a normal track would probably be seven tenths," said team boss Toto Wolff.

"But at least the car behaves no worse than before the updates, which considering the Monaco factor is not bad at all."

Lewis Hamilton agreed: "I can feel the improvements, even if we are not as close as we would like."