Mercedes head of motorsport Toto Wolff has acknowledged the team took a gamble by choosing to run a new engine at the Italian Grand Prix.

Nico Rosberg was forced to retire from Sunday's race at Monza, enabling team-mate Lewis Hamilton to open up a 53-point lead in the drivers' championship with victory.

An ageing power unit was cited as the cause for Rosberg failing to finish, with Mercedes forced to turn back to a unit that had already completed five race weekends when the German's new engine was contaminated by a leak in the cooling system during qualifying.

Reflecting on Mercedes' decision to utliise a new engine, Wolff is quoted by Autosport as saying: "We brought that phase four engine because we wanted to understand if that direction of development was the right one.

"It was a bit of a risky call and we saw what happened to Nico. That was the result of that engine - the reliability runs were on quite a high mileage but they weren't finished yet."

Wolff highlighted forward planning as a key factor in Mercedes bringing in a modified engine at Monza.

"It's not a pure performance factor but there are other things behind it," he added.

"In hindsight, yes we lost a car and Nico lost valuable points, but this is a competitive championship, it's going to be one next year.

"So I think the earlier you can understand which direction you need to go development-wise, the better it is.

"We don't know yet whether it [Rosberg's latest engine] is terminally damaged.

"To make the point, it wasn't an engine failure we had, it was a leak in the cooling system which led the engine to fail."