George Russell's title hopes have taken another hit as Mercedes confirms a grid penalty for Singapore.

In his preview to this weekend's race, Toto Wolff confirmed that the British driver will require a new engine following his retirement from last Sunday's Bahrain Grand Prix.

"It will mean starting from the back of the grid on Sunday," said the Austrian. "That is particularly frustrating given the way he drove last weekend and the result he deserved to be fighting for.

"Unfortunately, these things are part of the sport," he added, "and our focus now is on giving him the best possible car and opportunities to fight back through the field."

Other than Russell's retirement, just a few laps from the chequered flag and an almost certain podium, the German team left Sepang baffled by the failure of its much-anticipated upgrade.

"We have spent the days since (Sepang) working hard to understand why our performance was not where it should have been," said Wolff. "We have identified several areas we need to investigate further, but F1 doesn't offer simple answers and we need more evidence before drawing firm conclusions.

"Singapore gives us an immediate opportunity to continue that work. The characteristics of the circuit are very different and that will help us build a clearer picture of where we are.

"That is why we will evaluate both the latest update package and our previous specification across the weekend to ensure we fully understand the direction we need to take."

With only one practice session - this being a Sprint weekend - running back-to-back evaluations seems risky.

Russell had been expected to take a grid hit in Austin, where overtaking is easier, certainly compared to Singapore, when he was scheduled to take on the ADUO upgrade, however last weekend's retirement means that the move has been brought forward.

That said, Mercedes has yet to confirm if the Briton will have the upgraded unit this weekend or an older-spec engine.

Speaking in Sepang, deputy team principal Bradley Lord warned that Russell may have to take another penalty at Austin in order to have the upgraded unit.

Russell goes into the Singapore weekend 84 points adrift of his teammate, who, it is understood, could put the title out of reach as early as Austin.