Chief executive Paul Jackson, audience development director David Andrews, sales director Nick Hewat and finance director MJ Olare are believed to face heavy financial penalties if they leave before the end of the year. All staff have been offered a cash reward for staying on until that time.
The deal is designed to reassure potential investors that there will be senior people in place to run the business following a sale.
The news will dampen rumours of Hewat following former boss Fru Hazlitt from Virgin to GCap after the resignation of GCap commercial director Duncan George - rumours that are still rife in the industry, despite last week's denial by GCap in Media Week.
An industry insider said the deal was "absolutely the right thing to do" and cited the merger between GWR and Capital Radio Group as the reason for such agreements.
"In that situation, the two cultures clashed enormously and they struggled to maintain the brand," he said. "Virgin is out there on its own as a radio station so it's vital the brand and culture continues and for that they need to keep the top team in place."
SMG chief executive Rob Woodward is preparing to address the market later this month at the end of his 100-day review since taking on the job.
He will talk about the future of the business, but is not thought to have planned any firm announcements about Virgin Radio, which is also considering floating on the stock exchange.
Radio owners have balked at the £100m price tag on Virgin Radio, with one insider saying this week that is not worth half that amount.
Early indications are that the Virgin Group could make a move for the station, with backing from private investors, or that UTV, the company that nearly bought Virgin earlier this year before merger talks collapsed, could make another bid for the station.
Chrysalis Group is also experiencing uncertainty as it awaits the outcome of its strategic review this summer.
In a separate development, Virgin Radio has hired CBS Outdoor's Giles Darby as head of agency sales in charge of strategy.
Darby joined CBS's agency sales team two years ago from Emap Advertising where he developed and launched the company's digital radio advertising offering.
MJ Olare
Virgin Radio moves to keep senior staff
LONDON - SMG has locked in Virgin Radio's senior management with financial incentives as it attempts to sell the station.