By Jonathan Legard BBC Radio 5live Football Correspondent

Jose Mourinho's three-year career as manager of Chelsea ended suddenly on Thursday.

The club announced that the relationship between the coach and billionaire owner Roman Abramovich had broken down.

The BBC's Jonathan Legard looks at the issues behind the departure of Mourinho, who has been replaced by the club's director of football Avram Grant.

Why wasn't Roman Abramovich happy with Mourinho?

Abramovich had become frustrated by the lack of swashbuckling football Chelsea were playing. He wants Chelsea to play with style and adventure.

In Mourinho's first season they landed the Premier League title with a brand of exciting football, with Damien Duff and Arjen Robben on the wings, scoring goals, thrilling crowds and beating Barcelona.

Abramovich was unhappy with the lack of entertainment on offer

That swashbuckling style has not been forthcoming since then.

Abramovich wants the stadium to be full and he wants to see people enjoying the football his team provides.

To see the ground half-empty this week really rankled with him.

Jose Mourinho, on the other hand, is all about results. If it is achieved with style that is a bonus, but victory is all and Abramovich has found that hard to take.

He has also become frustrated by Mourinho's ego. He didn't like the fact that he was getting involved in so many controversial scrapes - the spats with Arsene Wenger and not shaking hands with Rafael Benitez.

He thought it was lowering the tone and that was one of the planks of supposed reconciliation in the summer.

But toning it down is not Mourinho's style.

What about the impact of Mourinho's relationship with Shevchenko?

The owner was shocked by Mourinho's criticism of Andriy Shevchenko, who is like a brother to Abramovich.

He does not believe the striker was shown enough respect and felt the manager did not help his introduction to English football.

606: DEBATE Give your thoughts on Mourinho's departure

That's why he brought in Avram Grant - to give Shevchenko the support he wanted and that one-to-one coaching and attention.

Even in the last week Mourinho was dismissive of Shevchenko telling him he needed to improve.

Here was a player who has won the Golden Boot in Europe and is one of the world's most fearsome strikers, and he was being treated like Salomon Kalou.

Was Avram Grant moved in as director of football by Abramovich deliberately to fill Mourinho's boots?

It certainly appears very convenient considering he was sized up for the role for some time, and it certainly inflamed the relationship between Abramovich and Mourinho.

If Abramovich really was serious about sorting out their problems he would not have brought him in.

Mourinho found it unsettling and unnecessary to have this appointment.

He is a European Cup-winning coach, has won Premier League titles and is one of the brightest coaching talents of his generation.

He did not need any help - now three months later Grant is in charge.

What about the reported row between John Terry and Mourinho?

I understand there were words between the two, but I do not think that was the straw that broke the camel's back.

What will be interesting is the relationship between Avram Grant and the players.

Mourinho missed out on the Champions League

For all the occasional training ground arguments, Jose Mourinho was revered and appreciated by the squad.

He was a galvanising force and an inspiration and now he has gone.

Didier Drogba is said to have burst into tears when Mourinho came in to speak to the players.

We saw how much faith Mourinho showed in Drogba and he repaid him last season.

The concern for Chelsea is how much the breakdown between the owner and coach will impact on current players, particularly with contract talks currently ongoing with Frank Lampard.

Is Abramovich surrounding himself with friends and "yes men" and is that the best way forward?

As one source said to me, Chelsea could become England's equivalent of Hearts - a billionaire owner who buys the players, picks the team and allows a friend to play with the tactics.

Chelsea are becoming his team on the pitch as much as his club.

Abramovich has his own scouting system, which was another cause for concern for Mourinho.

The manager did not want to buy the likes of Shevchenko, Khalid Boulahrouz and Alex and did not want William Gallas and Robert Huth to be sold.

What happens if Chelsea's results do not improve?

Someone close to the club has predicted meltdown if results go wrong against Manchester United and Valencia.

The Champions League is of huge significance in particular as the final is in Moscow and where best to show off his mighty Chelsea than back home in Russia.

They have got off to a sticky start and cannot afford to slip up against Valencia, which was the scene of such a resilient performance last season when they won 2-1 to go through to the semi-finals.

Can you see Abramovich walking away?

Not at the moment. If anything you could argue he has the club just where he wants it - he is firmly in charge and calling the shots in the boardroom and the dressing room.

If he is still determined to win the Champions League twice in the first 10 years of his dynasty, the responsibility is falling squarely on his shoulders.

He has got rid of the man who has the pedigree you need to achieve his ambitions.

He has replaced him with someone whose record does not compare and there has to be a suspicion he is Chelsea's answer to Les Reed at Charlton last season.

I could be proved wrong - Grant's Israel side remained unbeaten in their World Cup qualifiers, but his only victories were against Cyprus and the Faroe Isles.

Is that sufficient to take on the likes of Manchester United, Barcelona and AC Milan?