Russia's national football team wished Serbia good luck in their World Cup campaign, which they kick off later on Thursday against five-time champions Brazil.
Russia and Serbia have warm ties, although last September president Aleksandar Vucic said Belgrade would not recognise the results of referendums held in four regions of Ukraine partly occupied by Russian forces.
"Good luck at the World Cup. We believe in your success brothers," the Russian team, who were not allowed to take their place in a qualifying playoff because of a FIFA ban over Moscow's invasion of Ukraine, wrote on their social media accounts.
At the Lusail stadium, some Serbia fans are expected to carry Russian flags.
According to regulations, they are allowed to do so, but none of the flags can bear Russian military symbols.
Flags have been thoroughly checked at the Qatar World Cup, which started last Sunday.