Mercedes team principal Toto Wolff has blamed the Silver Arrows' struggles at the Dutch Grand Prix on an upgrade to the floor of the team's car.

Mercedes enjoyed a mid-season resurgence, triumphing at three of the last four races prior to the summer break, following a difficult start to the year.

Lewis Hamilton was victorious at the British and Belgian grands prix after team-mate George Russell triumphed in Austria, but neither driver was competitive in Zandvoort when the season resumed on Sunday.

Russell finished seventh and Hamilton was one place further back after qualifying in 12th, as McLaren's Lando Norris claimed a dominant win to close the gap to drivers' championship leader Max Verstappen.

Mercedes used a new floor for the race after abandoning the planned change at Spa, and Wolff admits the team may have got things wrong.

"I think these cars are a surprise-box. We've had six podiums in a row and that doesn't look like the car three weeks ago that was first and second," he told Sky Sports.

"You can't really end up with a result like this without any major factor playing in, and that's something we need to analyse in the next few days before Monza.

"Was it because we put something on the car that didn't help? Did we engineer something into the car that wasn't good?

"Then how do you justify these swings of performance? Sometimes we looked really good this weekend and then obviously today, in terms of degradation, that was not very impressive.

"Was it a setup? Was it the track? What is it that we got wrong? Was it the floor that we put on the car? Was it all of this together?

"So, hopefully we can sort it out until Monza and become competitive again. But the swing in performance from P1-P2 and P7-P8, there's a biggie in there. It's not something that was simply a setup decision in my opinion."