The Tottenham full-back opened as a 33-1 rank outsider for the award but a string of big bets saw him move quickly to 5-6 favourite before most of the high street bookies closed the market.
"Enough is enough. After punters began trying to get £1000 bets on Kyle Walker to win Young PFA Player of Year we've closed the market," said William Hill media relations director Graham Sharpe on Twitter.
"Forgive me for being cynical, but I can't help but think the already decided outcome of Young PFA Player of the Year may have been 'leaked'!"
Walker is arguably the lowest profile name on the young player shortlist which also contains Manchester City star striker Sergio Aguero, who was also nominated for the senior award, and Walker's team-mate, Gareth Bale, who won the senior award last season.
Other high street bookmakers confirmed they were getting similar requests to put money on Walker before closing their books.
“We did close the book. It’s just about us exercising caution,” Alex Donohue of Ladbrokes was quoted as saying in the Mirror; Paddy Power's Darren Haines added: "There were unexpected lumpy bets on Kyle Walker and we closed the betting.”
Also on the shortlist for the award are Manchester United's Danny Welbeck, Chelsea's Daniel Sturridge and Arsenal's Alex Oxlade-Chamberlain.