The world's top soccer players and thousands of foreign fans are set to converge on Russia for the World Cup from June 14 to July 15.
Kanu, 41, who played for Arsenal and captained Nigeria's national side, travelled to Russia to play a friendly organised by FIFA in Kaliningrad, one of the 11 host cities, alongside former England international Wes Brown and former Brazilian international Cafu.
He flew from London to Moscow's Sheremetyevo airport before taking a connecting flight to Kaliningrad, the regional centre of the Russian exclave in Europe bordered by Poland and Lithuania.
He reported the missing cash when he arrived at his hotel and discovered it was not in his luggage. It was not immediately clear why he was carrying that amount in cash.
Police said they had detained two men on Sunday who had handled check-in luggage for a flight from London to Moscow.
"The stolen money has been seized and will soon be returned to its owner," Irina Volk, a police spokeswoman said in comments on the Interior Ministry website.
Police did not name Kanu in their statement, but the police press service told Russian news agencies Kanu was the victim of the theft.
(Writing by Tom Balmforth; Editing by Hugh Lawson)
