The 23-year-old has been in good form this season with seven goals to his name.
QPR boss Harry Redknapp was in Amsterdam in midweek to cast his eye over the Icelander as Ajax came up against Feyenoord in the Dutch Cup.
Ajax have refused to completely rule out a switch, admitting that any good offer would be considered.
Director of football Marc Overmars said: "If there are good transfer fees offered, we may not close our eyes to it."
However, the striker's brother and agent, Adri Sigthorsson, told Algemeen Dagblad: "Kolbeinn won't leave Ajax for a club from the English Championship.
"Sigthorsson is staying where he is."