Heathrow's largest shareholder Ferrovial has frozen investment in the UK as it waits to see how Brexit will pan out.
Rafael del Pino, the chairman of the group, said the firm was putting on the brakes for the time being, and would not be rushing decisions either way.
"We do not invest more in the UK, but we do not divest either," he said at the group's general meeting of shareholders.
Del Pino said the company viewed the process "prudently", not just because of its effect on the UK "but also throughout Europe", as nobody knows how Brexit will unfold and the consequences it will have.
Ferrovial, which also owns stakes in Glasgow, Aberdeen and Southampton airports, makes around 30 per cent of its revenue in the country.
He did though, add that Britain leaving the European Union may have "positive side effects", including the "most favourable attitude" of the government to expand London Heathrow Airport.
Last month, the London airport announced its shareholders, including Ferrovial, Qatar Investment Authority, GIC and the China Investment Corporation, were pressing ahead with plans to invest an additional £650m into the airport over the course of 2019.
A public consultation on a third runway at Heathrow ends on 25 May and later this year, or at the beginning of next, MPs will be asked to vote on the runway expansion.