The Telegraph claimed Malaga boss Manuel Pellegrini was set to take over at Eastlands. His price duly collapsed in the next City manager market and by Sunday evening the books had closed.
By Sunday night, Pellegrini was no better than BetVictor's 1/7 to succeed Mancini with Sky Bet in at 1/12.
Their David Stevens said: "We went 1/4 that Roberto Mancini would not be in charge at the Etihad at the start of next season following his side's shock Wembley defeat to Wigan, and 5/2 that he would survive, but all the money came at odds-on, before we made the decision to suspend the market, and this was followed by the first reports that the Italian could go as soon as this week.
"Billionaire football club owners do not accept trophy-less seasons it seems, with Manuel Pellegrini already lined up to step into the hot-seat, meaning the next Premier League season could start with new managers at Manchester United, Manchester City and Chelsea."
The fact that Mancini may be on his way out comes as no shock to most and comes in the wake of City's FA Cup final 1-0 defeat to Wigan on Saturday.
The also failed to defend their Premier League title this season and, for the second year in a row, were eliminated in the group stage of the Champions League.
After Saturday's Wembley defeat, Mancini criticised the club hierarchy for not saying anything about recent speculation - Pellegrini was linked with his job at the end of last week.
Betting expert Joe Ross from www.footyinsider.co.uk added:
'When the bookies close their stachels - you know something is happening. The layers don't like to stop taking bets on a vibrant market, which this is. The information coming out of the club must be rock solid and mancini may well be gone before City's last game of the season.'
He said: "If it is true I am stupid because I didn't understand anything.
"You have been speaking about this for the last six months, and also the last two weeks. It is too much.
"The club didn't stop this. I don't think that was correct.
"I don't think it is true."
It has been suggested the Italian could be out of a job before the Blues face Reading at the Madejski Stadium on Tuesday