Concern has been expressed after a bookmaker paid out thousands of euro to three punters who wagered on the specific time of Chelsea captain John Terry's first-half substitution against Sunderland at 100-1.
Paddy Power accepted the bets on Terry being substituted between 26:00 and 26:59 in Sunday's Premier League match, his last as a Chelsea player at Stamford Bridge.
The relegated Black Cats were aware of the orchestrated plan, which Terry has said was his idea, and the Premier League is understood to be relaxed about the matter, which did not contravene its rules.
News has emerged of to two customers of Paddy Power, who won €2,900 and €1,200 respectively.
The Football Association is yet to comment on the matter but it is understood there has been communication with betting companies, with the national governing body requesting any relevant information.
There is no suggestion that the decision to substitute Terry was anything other than an attempt by Chelsea to give their long-serving captain a farewell to remember in front of the club's supporters.
However, independent sport integrity commentator Chris Eaton says bookmakers should have been warned ahead of the orchestrated move.
"If the manipulation of play to create the substitution and honouring opportunity was officially sanctioned, no problem except that the sport bookmakers should have been warned and could have avoided losses," Eaton, a former head of security at FIFA and former head of operations at Interpol.
"There should be no unsanctioned manipulation of the free flow of competition permitted by the rules of the game.
"Play and competition without fail should be honest, clean and earnest."
Paddy Power said in a statement on Monday: "We replied to a novelty request for odds on John Terry's substitution - one of hundreds on the Chelsea game - and fair play to the three punters who were on at odds of 100-1.
"To be honest the only mistake here is we should have clocked sooner there'd be another cringe-worthy Chelsea send-off for JT."
Terry's substitution was forecast on social media by the Chelsea fanzine editor before kick-off.
Terry revealed after Chelsea's 5-1 win that the idea to come off in the 26th minute had come from him, to tie in with his squad number of 26.
There was a precedent at Chelsea. Didier Drogba was carried off by team-mates midway through the first half of his farewell appearance - also against Sunderland on the day Chelsea lifted the Premier League trophy.
One punter who attended the game predicted something similar regarding Terry and made an enquiry with Paddy Power before placing a €30 bet on the phone.
The punter, who wished to remain anonymous, said: "We thought maybe 10-1, 15-1 at most as there was a precedent set (by Drogba's substitution). I consider myself relatively lucky."
