The 23-year-old had an operation on Monday night to remove an area of scar tissue around the break.

After a long and strenuous rehabilitation programme, the former Norwich and Crewe star suffered a succession of frustrating setbacks in his attempt to reach full fitness.

And after West Ham's medical staff sought the advice of independent specialists, the decision was taken to solve the problem with an operation.

The recovery time is expected to be six weeks before Ashton can run again, meaning he will not be fit for a return to competitive football this season.

But he is hopeful he will be completely ready to resume full pre-season training this summer.

Hammers head physio Steve Allen told the club's official website, www.whufc.co.uk: "Dean underwent a successful diagnostic arthroscopy operation on his left ankle to remove a significant amount of scar tissue - a problem directly linked to the original injury.

"We left no stone unturned to get Dean back out on the football field as soon as possible, but it was clear he had gone as far as he could with the methods that had been used.

"The only remaining option was to have another look at the injury site.

"We sought the opinions of the leading ankle specialists in the country and, following their advice, the decision was made to operate."

Ashton scored six goals in 14 matches last season, including one in the FA Cup final thriller against Liverpool which West Ham lost on penalties after a 3-3 draw.

His continued absence is another blow for manager Alan Curbishley who has won only two games out of 13 in the Barclays Premiership since taking over from sacked Alan Pardew in December.

But Curbishley has seen it coming after Ashton returned to training last month and yet was not considered fit enough to play even in reserve matches.

One from bottom in the table, West Ham face a major task to escape relegation with just eight games to go against the likes of Arsenal, Chelsea, Everton, Bolton and Manchester United.

The shadow of a points deduction over their controversial signings of South American pair Carlos Tevez and and Javier Mascherano, with the latter subsequently transferred to Liverpool, still hangs over Upton Park.

But their luck appeared to have turned last Saturday at Blackburn when a dubious penalty and the Bobby Zamora winner, which video evidence proved did not cross the line, sealed three vital points.

And after seeing his side fight back from being a goal down at Blackburn Curbishley insisted: "It's not over yet.

"The last two performances have given us a bit of hope. We live to fight on against Middlesbrough (at home a week on Saturday).

"If we can get two wins on the bounce it could really change the shape of things.

"I'm just pleased with the three points (at Blackburn). You have to live and die by decisions and we have been on the receiving end of a few this season."

Curbishley still has more than a week before the Middlesbrough match and said: "It gives us the opportunity to get a few players back from injury such as Matty Upson, Calum Davenport and Nigel Quashie."

And centre-half Danny Gabbidon, last season's player of the year, could also be in contention despite being ruled out of Wales' Euro 2008 qualifier against Republic of Ireland on Saturday.

Gabbidon ripped a tendon off a groin muscle against Fulham in January and has not played since, but the fact he reported to the Wales training camp this week points to his returning fitness.