* Benitez leaves after shock outburst about lack of signings

* Leonardo or Zenga favourites for role, Spalletti unlikely (adds details, byline, quotes)

By Mark Meadows

MILAN, Dec 23 (Reuters) - Rafael Benitez’s reign as Inter Milan coach ended in ignominy on Thursday when he left the European champions after just six months in charge having dared to question club owner Massimo Moratti’s authority.

“Inter and Rafael Benitez announce that, mutually and with satisfaction on each side, they have reached an agreement for the early resolution of his contract,” said a statement from the Serie A club after days of talks.

“Inter thank Rafael Benitez for his work with the team which led to Italian Super Cup and World Club Cup success. Rafael Benitez thanks Inter for a great professional experience and the victories obtained together.”

The Spaniard, appointed in June after treble-winner Jose Mourinho left for Real Madrid, was already on shaky ground with his team slumping to seventh in Serie A and spluttering through the Champions League group stages.

He had appeared to secure his job with Saturday’s World Club Cup triumph, only to explode in the post-match news conference and threaten to discuss his future with his agent if signings did not materialise in the January transfer window.

Benitez directly criticised Moratti, saying he was promised buys in the close-season which did not arrive and pointing out that the club recruited five first-teamers last term under Mourinho and yet did not bring any player in for him.

His ultimatum was too much for Moratti, a man not known for his patience, especially as it came when the president thought his side should be celebrating a fifth trophy of a great year rather than pondering his outburst.

Former Liverpool coach Benitez knew when he took the job that Italian soccer worked differently from English with the clubs rather than the coaches buying players.

He even said he saw this as positive element of the move having left Liverpool after six years in which his transfer spending at Anfield was heavily criticised by fans and media.

However, a raft of early injuries at Inter, which some pundits blamed on his new training regime, meant Benitez was down to the bare bones by late October and the lack of signings rankled with him more.

SPALLETTI STAYING?

The former Valencia boss had become increasingly militant at Liverpool after a quiet start, famously lambasting Manchester United manager Alex Ferguson in a news conference before using bizarre Spanish proverbs about milk, sugar mountains and priests to criticise his ex-Anfield bosses when he arrived at Inter.

His blast at Inter was a step too far for the Italians, though, given they were his current employers and he now finds himself out of work while Inter begin the task of replacing him knowing they do not have a game until Serie A resumes on Jan. 6.

Zenit St Petersburg coach Luciano Spalletti was tipped by media and bookmakers to take over but the Russian champions have said the former AS Roma boss is staying.

Former Inter goalkeeping great Walter Zenga is therefore the a new favourite along with ex-AC Milan boss Leonardo, whose former side are now top of Serie A in a galling reminder to their city rivals of how far they have fallen since May’s treble.

Their chances of a sixth straight Serie A title look remote whoever takes over as Inter lie 13 points behind Milan.