Stephen Ferris will miss the first four months of the season after agreeing a six-month extension to his Ulster deal in an attempt to regain full fitness.

The short-term contract sees the Irish flanker remain at Ravenhill until at least the end of 2013 after he rejected a lucrative option to play in Japan.

The 27-year-old had a third operation on his ankle in May and will now undergo rehabilitation with Ulster.

Ferris has not played since suffering the ankle injury in early November.

The 35-times capped Ireland international, who has been plagued by injury in recent years, will work with the medical and strength and conditioning staff at the Irish province with the aim of making a full and complete return to rugby.

He is not expected to make a comeback until at least the start of 2014, ruling him out of the first half of Ulster's season and Ireland's autumn international series of matches.

The back row forward has played 102 times for Ulster and toured South Africa with the British and Irish Lions in 2009.

Ferris's contract with the Irish Rugby Football Union had been due to expire on 30 June and a move to Japan had been mooted as a possibility.

He missed Ireland's entire 2013 Six Nations campaign and last November's internationals because of the injury.

In April, Ulster coach Mark Anscombe had admitted that he was resigned to losing Ferris, at which point an unnamed Japanese club were thought to be favourites to secure his signature.

Commenting on the contract extension, Ulster's Director of Rugby, David Humphreys, said: "Stephen has had a difficult year with the injuries that he has suffered, but when he is fit, there is no doubt that he is one of the best back-row forwards in the game.

"Stephen is passionate about playing for Ulster and Ireland and our aim in giving him this contract extension is to provide him with the best possible care to enable him to get back playing."

"I am delighted that I can continue my recovery and rehab from injury within the Ulster Rugby set-up," commented Ferris.

"I believe that working with the medical team at Ulster, along with the excellent strength and conditioning coaches, offers me the best chance of regaining full fitness and of representing Ulster and Ireland again."