The Manchester City manager, Roberto Mancini, held extensive negotiations with Monaco with a view to joining the club at the end of last season. The talks, lasting almost three months, led to Monaco believing he would join them and can be revealed for the first time.

The details of the extraordinary negotiations have been disclosed to the Guardian, corroborated at the highest level, and suggest that Mancini was close to accepting Monaco's offer, before opting to stay at City when his team overhauled Manchester United to clinch their first title since 1968.

The five-year contract, put forward during a meeting in Rome, was tax-free with Monaco's majority shareholder, the Russian billionaire Dmitry Rybolovlev, willing to pay Mancini €8m (£6.4m) a year, plus substantial bonuses, if he left the Etihad Stadium. Rybolovlev, ranked 100th on the Forbes list of billionaires, bought his majority stake in Monaco in December 2011 and is determined to use his wealth to return the club to the Champions League after a difficult period in which the 2004 finalists have dropped into Ligue 2.

Mancini was involved in secret talks and tempted with a deal that would have meant there were only two other managers in the world, Carlo Ancelotti at Paris Saint-Germain and Guus Hiddink at Anzhi Makhachkala, on higher salaries.

Mancini eventually signed a new five-year contract at City in July, but not before Monaco had formed the distinct impression he was willing to sever his ties with his current club.

The Italian is hugely popular with City's supporters, winning the FA Cup in his first full season after replacing Mark Hughes and following that by steering them to the league title. His position has started to come under scrutiny recently because of City's difficulties in the Champions League, and briefly did so at one point towards the end of last season. Until now, however, there has never been any indication that, at any stage, he has already been considering his next move.

It may be that Mancini, who declined to comment, was simply hedging his bets in case he lost his job at the Etihad Stadium and regarded Monaco as the next best alternative. The information supplied to this newspaper, however, states that all terms of a prospective contract with Monaco had been agreed. Monaco, in short, were convinced they had got their man.

The negotiations began at the turn of the year, according to high-level sources with access to the figures involved, and the final meeting took place in Rome shortly after the 1-0 defeat for City at Arsenal in early April, a result that left Mancini's team eight points behind United in the title race.

Mancini accepted after that game that City had all but lost the league and in the coming days well-placed sources confirmed that his position could not be guaranteed and would be reviewed at the end of the season. Mancini's job was described as potentially at risk should City tail off in the final six games and finish even further off the top.

Instead, United surrendered their lead and City won the title courtesy of Sergio Agüero's stoppage-time winner against Queens Park Rangers in the final game. It was after that victory that Monaco were informed Mancini was no longer interested in their vacancy. The seven-times French champions appointed Claudio Ranieri two weeks later on a two-year deal, with the option for a further 12 months, saying "he clearly emerged as the outstanding candidate". Stefano Pioli, the Bologna coach, was also discussed when it came to replacing Marco Simone. Mancini, however, was the first choice.

Rybolovlev took over at Monaco at a recent nadir in their history, with the club bottom of Ligue 2 and in serious danger of falling into the third tier of French football. They recovered to finish eighth last season and Ranieri has taken them to the top of the table 12 games into the new campaign.

Mancini, who was also prominently linked with the Russia national job before Fabio Capello's appointment in July, has continued the business of trying to turn City into the major force of English football. City are third in the league, unbeaten after nine games, but have only a solitary point from their three Champions League fixtures against Real Madrid, Borussia Dortmund and Ajax and sit at the bottom of their group, facing the distinct possibility they might not even qualify for the Europa League.

At the same time City, who also declined to comment, have appointed Txiki Begiristain as their new director of football. Begiristain previously worked at Barcelona, as did City's new chief executive, Ferran Soriano. That, in turn, has led to increased speculation about Pep Guardiola's potential availability at the end of the season.

The revelations about the Monaco job are not linked to that but, equally, they will not help Mancini when it comes to his relationship with the relevant people in Abu Dhabi. The club's owners are known to be concerned about the team's failures in Europe, but Mancini's difficulties have been predominantly with Brian Marwood, the club's football administrator with responsibility for transfers, and the previous chief executive, Garry Cook. Marwood's role has been changed to that of academy director after the appointment of Begiristain.