Mourinho was opposed to Grant's appointment in the summer

The Israeli, who was the club's director of football, will take charge alongside Steve Clarke.

"The club is delighted that in Avram we have an experienced man who can come in at a difficult time," said the club.

BBC Sport revealed the news on Thursday morning as Mourinho said an emotional farewell to players at the club's training ground in Cobham, Surrey.

Interview: Milan Mandaric on Avram Grant

Report: Mourinho leaves Chelsea

Mourinho's first season at Chelsea

Mourinho was then seen driving away shortly before the statement confirmed his successor.

The statement added: "In Steve we have a Chelsea man and he will be a crucial part of the management team going forward. Avram and Steve have our full confidence and support."

I think he's ready for the job. It's a big job of course and whether he will do it better than Jose Mourinho I don't know. Manchester City boss Sven-Goran Eriksson on Avram Grant

Grant and Clarke took their first training session on Thursday and they were joined by club owner Roman Abramovich at Cobham.

Chelsea revealed the session was "sharp, with the players in buoyant mood, despite the disappointment of Tuesday's Champions League draw with Rosenborg."

The statement added: "Grant and Clarke, who have been appointed by the club's board, led a training session which included Wayne Bridge, back on the road to recovery."

Grant, 52, is due to be unveiled at a news conference on Friday and it is understood that his appointment is for the foreseeable future.

Manchester City boss Sven-Goran Eriksson is a friend of Grant's and backed him to make the step up to the manager's position.

"I think he's ready for the job," said Eriksson. "It's a big job of course and whether he will do it better than Jose Mourinho I don't know, but I will call him later and wish him good luck.

"He's very a good man," he added. "He knows his football and has a lot of experience. He did a good job with the (Israeli) national team."

In contrast former Chelsea player Pat Nevin believes the appointment will only be a short-term option.

"It's an absolute certainty to be a short-term measure because they can't get the man they want," he told BBC 5Live.

"And the man I'm sure they want is (Russia manager) Guus Hiddink. He's not going to be available until Russia are out of the competition at the Euros in 2008.

606: DEBATE Abramovich is now entering the most hazardous period of his Chelsea tenure Phil McNulty - BBC Sport

"Avram Grant is going to be as welcome as Camilla at Diana's memorial.

"This guy is not well-loved at Chelsea. He is not going to last."

Grant is a close friend of Chelsea owner Roman Abramovich and his summer arrival at the club came after opposition from Mourinho.

The Portuguese told Grant not to interfere with team affairs but the Israeli's position was strengthened with a seat on the board.

Leicester City chairman Milan Mandaric, who worked with Grant at Portsmouth where he was a technical director, said he faced a huge task at Chelsea.

"I don't think there are too many people who can step into Jose's shoes, but if people chose Avam, he deserves a chance to see what he can demonstrate," Mandaric told BBC 5Live.

Another former Chelsea player Gavin Peacock agreed with Nevin and said Grant would need to work hard to maintain team morale.

"If you're bringing in someone like Guus Hiddink, then you're bringing in someone of great repute, as for Grant, I don't know," he told BBC 5Live.

"I think the heart of the team will be affected by Mourinho's departure. It will be very difficult to get the team spirit that Mourinho managed to manufacture very quickly at Chelsea."

Before his arrival at Portsmouth, Grant guided Israel to the brink of World Cup qualification in 2006, having also coached Israeli sides Maccabi Tel-Aviv and Maccabi Haifa.

Avi Cohen, the chairman of the Israeli Professional Football Association and friend of Grant, backed the move, although he too said it came as a surprise.

"Avram Grant is very successful in Israel. He won the championship with several teams and he knows football," he said.

"Even so it is a shock that he was chosen. He had said that he had a very good position at Chelsea. He is a very good friend of Abramovich and he believes in him.

"I'm not sure that he won't be successful more than anyone else. If he has the ability he can be successful."