De Gea put in another top-class performance on Saturday in United's 2-0 win at QPR.
The Spaniard, who has 18 months left on his contract, has been linked with Real Madrid and reports over the weekend suggested the goalkeeper could be used in an exchange that would see Bale move to Old Trafford.
The Manchester United Supporters' Trust (MUST) asked United fans what their preference would be in a poll on their Facebook page.
MUST asked: "If you had a straight choice to either keep David de Gea or sell him as part of a player exchange deal for Gareth Bale with Real Madrid, what would you choose to do?"
Twelve hours after posing the question, MUST said "over 99 per cent" of the 600-plus fans who responded said they would prefer to keep De Gea.
"With this in mind it signals the challenge (executive vice-chairman) Ed Woodward and (owners) the Glazers have to get Manchester United's most popular player signed up on a new contract, before Real Madrid attempt to prise him away," a MUST spokesman said.
Source : PA