The candid assessment from Stuart Patrick comes as the report into the future of London's hub airports and the rescue of Prestwick by the Scottish Government have highlighted the importance of 2014 for Scotland's west coast airports.
Mr Patrick said: "We had 15 flights at that time, we are now at nine ... we want to cover that gap and get back to where we were. The critical issue is the choice and availability of onward connections - four out of 10 people on the London Heathrow flights are travelling onwards."
The airport has recovered only about 40% of passenger volume from the lost services, Mr Patrick added. "We can't quantify the impact but we can be fairly sure it has a long-term impact on the choices being made to bring events to Glasgow, to invest in Glasgow and to trade with Glasgow."
Unlike Edinburgh, which retained its Heathrow slots, enabling their transfer to Virgin when BMI was sold to BA's parent IAG last year, Glasgow lost its BMI services and slots after the airline withdrew its Heathrow service in January 2011. But while Edinburgh Airport (now independently owned) has voiced support for Gatwick, Glasgow Airport (still linked with Heathrow) has thrown its weight behind the campaign for an expanded Heathrow as London's primary hub airport, because of its importance for UK domestic feeder services.
"This is a long-term growth potential issue for us in Glasgow," Mr Patrick said. "We are not persuaded by Gatwick because it is not currently half of the scale of Heathrow and it is difficult to see how it could be." He said a 'Boris Island' new airport in the Thames estuary might have the capacity but "it would take decades to get to that stage, by which time most of the damage would have been done".
Fraser Grieve, of the Scottish Council For Development And Industry, said connections into Heathrow and Gatwick had been in decline from UK regional airports, which now had more services to Amsterdam than London. "The key issue for proposals for increasing capacity in the south-east is about domestic connections. Otherwise it just becomes a point to point airport for London."
Meanwhile, the loss to Prestwick Airport of its Stansted route in June 2011 was widely lamented as damaging to the local economy and tourism, and one of the factors that propelled it into Scottish Government ownership last year.
Councillor Bill McIntosh, leader of South Ayrshire Council, said: "The ultimate wish of the Scottish Government will be to return it to private ownership and for that to happen it really has to be a successful airport. From a south Ayrshire perspective I am keen we have a seat at the table, this is our local economy, and we are looking at things like route development."
On concerns from Glasgow that state ownership raises issues of competition and commercial confidentiality, Mr McIntosh said: "Glasgow is very well able to look after itself. It would not be making noises if Prestwick was no cause of concern, but there is a market for both airports in different ways and we can work in tandem."
Mr Grieve said the Government might be able to apply public service obligation or regional development support, but added: "The challenge is Prestwick's proximity to Glasgow."