Valtteri traded fastest times with Lewis in the morning, ending the session in P3, just behind Vettel. But like Lewis, the Finn had a tougher afternoon, managing just 10th on the leaderboard.
"Practice two was difficult and we struggled with the pace over one lap," said the Finn. "We made some changes between practice one and practice two but we clearly went in the wrong direction - that's why both of us were struggling.
"When the car isn't quite right you lose a lot of time in Monaco. We tried to go back with the set-up and it felt better but by that point we'd already put a lot of laps into the tyres. At least we've learned what not to do with the set-up here.
"It's a shame but we have a full day tomorrow to analyse everything and come back stronger on Saturday. It will be close again at the top I'm sure.