Running in second place behind leader Max Verstappen, Leclerc attempted to give third-placed Sergio Perez a slipstream in the final laps to help him pull clear of Russell, who was on course to give Mercedes second in its fight against Ferrari.
Perez needed to finish five seconds clear of Russell after being handed a five-second penalty for a clash with McLaren's Lando Norris.
But while Leclerc let Perez past into second, the Mexican was unable to pull clear of Russell and dropped from second to fourth after the penalty was applied post-race.
It meant Mercedes kept second in the constructors' championship by three points.
"It was all in the last few minutes because Checo had five-second penalty," Leclerc explained his assistance to the Red Bull driver.
"We had to help him in a way for him to finish in front of George with the five seconds. I tried to give him the DRS and a slipstream, but that unfortunately wasn't enough.
"It is just a shame that we finished third in the constructors' [championship]. That's all that mattered to me in this end of season, and we didn't achieve that."
Source: Autosport