The Spanish owner of Heathrow Airport is understood to have made a bid to buy Glasgow, Aberdeen and Southampton airports.
Ferrovial, a Madrid-based conglomerate, is reported to have lodged an £800 million takeover bid for the three airports, according to news agency Reuters.
The airports are currently owned by Heathrow Airport Holdings, formerly known as BAA. Ferrovial owns Heathrow and has a 25% stake in HAH.
Ferrovial was reported to have sounded out the HAH board about acquiring the three regional airports outright in December.
Gatwick owner Global Infrastructure Partners has also been linked to a potential purchase of Aberdeen airport.