Mexican Perez only joined the team from Sauber at the start of the current season.
"We haven't confirmed our driver lineup. We haven't signed contracts with drivers," Whitmarsh told reporters.
"We are still talking about that. There has been a lot of honest feedback both ways, which is best done in private not in public. We'll see in the future."
Magnussen, who won the Formula Renault 3.5 feeder series this year, would become the first rookie taken on by the British team since 2007 when Lewis Hamilton stormed onto the F1 scene.
Elsewhere in F1 today, Williams announced that Felipe Massa would would replace Pastor Maldonado for next season.