1. He has failed to solve Chelsea's problems
Carlo Ancelotti has had two months to integrate Fernando Torres into the team, but he has chopped and changed tactics in a hit-and-hope method of making it work, to no avail.
In hindsight his decision to start with Torres instead of Didier Drogba at Old Trafford could be the one that haunts him.
On the big nights, Ancelotti is conservative in both his tactics and his substitutions. Needing a goal with nine minutes to go against United, Ancelotti put full-back Paulo Ferreira on to replace Alex, when Yossi Benayoun was available. Chelsea fans have been critical of his cautious substit-utions for some time, but Ferreira's introduction in the 81st minute on Tuesday was the most galling.
Ancelotti also did very little when Chelsea's form deserted them at the end of last year. His policy of playing it cool can quickly seem like an inability to take action when it is required.
2. Four defeats in four big European games
Ancelotti's record of twice leading Milan to the Champions League was behind Roman Abramovich's decision to appoint him, but, at Chelsea, he has failed on the biggest stage. Chelsea lost both legs against Internazionale in last season's knock-out stage and then lost both games against Manchester United again in this year's quarter-finals.
In two seasons under Ancelotti, Chelsea have a record of four defeats in four games as soon as they meet one of the Champions League contenders. Given all the money Abramovich has spent, he clearly expects more. It is tough on Ancelotti to always compare him to Jose Mourinho, but that didn't happen to him in his time at Chelsea.
3. Ancelotti has looked a weak leader this season
Luzi Felipe Scolari was sacked when he lost the trust of Chelsea's senior players. Ancelotti is still popular with his players, but importantly some respect for him has gone in the past six months. The Italian lost some face with the squad when he did not stand up to Abramovich over the decision to sack his close friend Ray Wilkins last November, which was in contrast to the way Mourinho had fought for his assistant Steve Clarke a few years earlier.
The £50m signing of Torres has also served to undermine his authority, for although the Italian denies it is the case, it looks from the outside that he is picking the Spaniard to curry favour with Abramovich. The players still back Ancelotti, but for some it is a case of "better the devil you know."
Three reasons why Chelsea might keep Ancelotti
1. All he needs to succeed is a bit more time
The most compelling argument is that all managers need time to build their own team -- even the likes of Alex Ferguson and Arsène Wenger needed time.
But since Abramovich took over in 2003, the revolving door at Stamford Bridge has not stopped.
The average life expectancy of a Chelsea manager is 417 days, and Ancelotti is already way over that, having lasted 651.
The Chelsea team, built by Mourinho seven years ago, is on its last legs -- the Double last season being a final hurrah of a great side -- and an overhaul is overdue.
The arrival of Torres, David Luiz and Ramires in the past year signals a change of direction for Chelsea, and Ancelotti deserves the chance to leave his own imprint on the new side.
He built a team at Milan that won the Champions League twice and there is no reason to believe he could not do the same at Chelsea.
He proved his worth by leading the ageing side to the Double last year, and deserves the chance to mould his own team.
2. A lack of alternatives
Mourinho has changed tack recently and is now talking about staying at Real Madrid. In February Pep Guardiola signed a one-year extension to stay at Barcelona until 2012.
Ferguson and Wenger are unobtainable. Guus Hiddink is halfway through a delicately poised Euro 2012 qualifying campaign with Turkey.
Many of Abramovich's preferred candidates would be hard to tempt out of their current positions.
But the Chelsea job is becoming an increasingly harder one to sell to potential candidates, partic-ularly with Uefa's Financial Fair Play Rules that start in 2012.
And at least Ancelotti is used now to coping with the whims of Abramovich and his entourage.
3. There is more to Ancelotti than just results
Abramovich's dream is a Barcelona in blue, and the closest he came to it was towards the end of last season, in which Chelsea scored 142 goals in 58 games. One of the reasons for sacking Mourinho was the lack of attacking football, but at their best under Ancelotti -- particulalry last season -- Chelsea were a joy to watch.
Ancelotti has also done much to improve Chelsea's image.
On the pitch, the snarling dissent of previous seasons has evaporated and the outgoing champions top the Fair Play League.