Brian Donohoe, the Labour MP for Central Ayrshire, said the lack of support by Infratil is damaging prospects of a sale and jeopardising its future.
He claimed the basic upkeep of the loss-making, no-frills airport had suffered following a decision by the company to put it on the market in March along with its other European airport, Kent Manston.
Mr Donohoe's comments come after the airport was forced to shut on Thursday evening, due to heavy rain, leading some flights to be diverted to Edinburgh.
He said a decision by the company to write off losses from both airports had produced a visible effect at Prestwick, whose "tired" appearance was noticeable to passengers.
"The basic upkeep of the airport is suffering. You can let it go for a while, you can get away with [a lack of investment] for a time but there comes a critical point at which it makes no sense and you'd be better off locking the door and walking away," he said.
"There is no investment going on, nothing that would suggest there is any positive future for the airport. It is very worrying."
Passenger numbers at the Ayrshire airport have tumbled in recent years following a move by Ryanair, the budget airline which provides nearly all the airport's passenger flights, to relocate many of its services to Edinburgh after overseeing rapid expansion during the noughties.
There were 1.1 million passengers passing through Prestwick in the 12 months to July, fewer than half the numbers seen only four years earlier, according to figures published by the Civil Aviation Authority.
Prestwick and Manston racked up losses of £5 million between them in 2011, the last year for which figures are available, according to Infratil, which described the airports as underperforming when it decided to sell them earlier this year.
Tom Wilson, chief executive of Infratil Airports Europe, admitted the sale of Prestwick, which is due to be completed by next year was progressing relatively slowly.
But he denied this was down to a lack of investment by Infratil. "It's no secret that the sales process is running relatively slowly, which is symptomatic of the general state of the economy rather than any particular investment policy Infratil has," Mr Wilson said.
"Aviation since 2008 has been at best static and in many places been in decline.
"It's a tough market to enter. It's fair to say that when a business if for sale, it's not likely that the current shareholder will be spending any more than they need to.
"Clearly it is a matter for any shareholder who purchases the airport to look at the size of the operation and decide on any investment that may be required."
Mr Wilson said there were a number of parties who had expressed interest in buying the airport but he would not name them or discuss any details of the negotiations.
And he added Ryanair was very pleased with its performance at Prestwick, despite difficulties in the aviation industry.
"As far as I am aware, Ryanair is still very pleased with its performance at Prestwick but that is in the context of the market being very tough and the Government's Air Passenger Duty making it very difficult for airlines," he said.
Though best known for being the main base in Scotland for Ryanair in the noughties, as a business Prestwick is more dependent for its income on air freight operations and aircraft maintenance hangers used by British Airways and Ryanair.
The airport's profits from air freight have been hit hard over the past decade as the volume of cargo it handles has fallen by 73% from a peak of 43,100 tonnes in 2001 to just 11,900 last year.