The 28-year-old British driver needs to use a new power unit following his dramatic retirement from last weekend's Bahrain Grand Prix in Malaysia. Russell qualified eighth but appeared on course for a podium finish before an engine failure forced him to retire from third place with only five laps remaining.
Mercedes team principal Toto Wolff confirmed that the team has no choice but to fit Russell with a new power unit this weekend. The change will push several components beyond their permitted allocation, resulting in a grid penalty.
The setback comes at a difficult point in Russell's season. His retirement last weekend allowed Mercedes team-mate Kimi Antonelli, who finished second behind Max Verstappen, to extend his advantage in the championship. The Italian now leads Russell by 84 points.
With six or seven races remaining, depending on whether Formula 1 receives the necessary security assurances to hold the Qatar and Abu Dhabi events amid the ongoing conflict in the Middle East, Russell's championship challenge has been severely damaged.
Wolff described the penalty as particularly frustrating given Russell's performance in the previous race.
"Unfortunately, these things are part of the sport," Wolff said, adding that Mercedes would focus on giving Russell the best possible car and opportunities to recover through the field.
The penalty is an especially significant blow in Singapore, where overtaking can be notoriously difficult. Although Russell still has a mathematical chance of closing the gap to Antonelli, his ability to reduce the deficit will be considerably harder if he starts from the back.
Mercedes was forced to make the change because Russell had no usable engines remaining within his allocation. Earlier reliability problems had left his available power units either damaged or with too much mileage.
Antonelli faced a similar penalty before winning the Italian Grand Prix last month. Russell's latest setback adds to a season marked by mechanical problems, despite his victory at last year's Singapore Grand Prix.
The Singapore weekend will also feature the sixth and final sprint race of the Formula 1 season. Russell's penalty applies only to Sunday's Grand Prix and will not affect Saturday's sprint.
Wolff said Mercedes had spent the days since the previous race analyzing its performance and would use Singapore as an opportunity to improve.
"We need to keep learning and score the strongest result we can with both cars," he said.
