Hearts have made an official approach for the South Korean striker Ahn Jung-hwan, his agent Tom Sanders has told BBC Scotland.
"Hearts said they would come back to me again at the end of the week," he said.
Sanders said representatives of the Tynecastle club, as well as Rangers and Celtic, would be watching the player in action on Sunday.
Jung-hwan and his South Korean team-mates were beaten 3-1 by Ghana at Easter Road in a World Cup warm-up.
Sanders said one firm offer had been made, from an English Premiership club.
