Information is being sought from bookmakers who claim to have paid out on bets struck at odds of 100-1 that Terry would be substituted in the 26th minute – matching his shirt number.
Following concerns that have been raised, the FA is trying to establish whether the bets were genuine.
The substitution itself was not a breach of FA rules. But it is forbidden for any participant in a game to share information from which others could profit financially.
A Chelsea fanzine on Twitter, @Onlyapound, stated at 6.24am on Sunday: “John Terry starts today and will be substituted in the 26th minute. #captainleaderlegend #wewillalwaysluvya”.
There is no suggestion, however, that the claim was made on the basis of information received from either Chelsea or from anyone connected with Terry.
Terry has admitted his 26th-minute farewell was his idea and he had agreed it with manager Antonio Conte.
Conte said: “He deserved this. He’s a legend of this club, not just this club but one of the best defenders in the world.”
But ex-England captain Alan Shearer said he was “not sure” about the timing of the guard of honour.
He told Match of the Day: “It was done with good intentions but I don’t think anything should be done that could undermine the integrity of the game.”
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,” said 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.”
FA rules regarding match-fixing state that: “Fixing is arranging in advance the result or conduct of a match or competition, or any event within a match or competition.”
Some commentators sought to make comparisons with the incident which saw substitute goalkeeper Wayne Shaw sacked by Sutton United for eating a pie during February’s FA Cup tie with Arsenal .
An investigation into the incident, dubbed ‘Piegate’ is ongoing.
However, the bet involving Shaw was offered on the open market by a bookmaker, whereas wagers on Terry’s substitution followed an enquiry by a punter.
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 £25 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.”
Another punter said he opened an account with Paddy Power in order to place the bet, which was only possible to do over the phone.
The Chelsea fan was not watching the game, but says he put on a £10 stake and received his winnings in his account on Monday.
“I only put money on this because I thought this is surely going to come in,” said the punter, who wished to remain anonymous.
“I don’t normally bet. It’s only the second time I’ve ever placed a bet. I was surprised the odds were that high.”
Terry’s substitution process began when the clock ticked on to 26 minutes – making it the 27th minute of the match – and by the time he left the field through a guard of honour formed by his team-mates it was the 28th minute.
Yet Paddy Power honoured the bets, saying: “Clearly the send-off was planned for the 26th minute to commemorate JT – hence why we paid out.”
Terry appeared for the Blues for the 717th time, starting in the Premier League for the sixth time this season. It was his 580th game as captain of the team.
The 36-year-old former England captain announced last month that he would be leaving Chelsea after 22 years following a peripheral role this season, but he leaves as a Premier League champion.
A 16th major trophy of Terry’s career could follow in Saturday’s FA Cup final with Arsenal at Wembley.
He could yet make a 718th appearance, although he is likely to be a substitute at best, before deciding whether to retire on play on elsewhere.