Russell has switched from his usual Williams seat to fill the space vacated by Lewis Hamilton as the world champion self-isolates following a positive Covid test after last weekend's Bahrain Grand Prix.
Asked what the Briton could achieve, Ferrari driver Leclerc replied: "For me, a podium at least. I have some hope for a win. It is very optimistic but I know that he is very good. I could bet on a win."
Leclerc and Russell have known each other for the best part of a decade, having risen through the junior ranks together in order to reach Formula One.
The pair were part of the 'Twitch quartet' that provided so much entertainment during the fallow months of the lockdown earlier this season along with Red Bull driver Alex Albon and McLaren's Lando Norris.
The Monegasque wished Hamilton well but feels the champion's illness has given Russell a great chance to further prove his worth on the grid after a season in which he has already demonstrated his talents despite driving backmarker machinery.
"I hope Lewis is ok and that he will recover quickly," added Leclerc. "For George, it is an amazing opportunity. I have known him for a lot of years. I was team-mates with Alex [Albon] and George back in 2011 in karting.
"Now, he finally has the opportunity to race for a top team. I don't know how long for, whether it will be for one weekend or two and I think he will show how good a driver he is this weekend.
"Of course, he has shown it before, but now having the opportunity to be fighting further up with the best car out there is a great opportunity for him and I hope he will do well."
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