“Following this, our medical team was unable to provide a satisfactory report regarding Joe’s fitness,” said Saints’ chief executive Allan Robson.

“As a consequence, the contract concluded earlier is no longer valid.”

“We are naturally disappointed that Joe will not be joining us and wish him all the best for the future”.

Van Niekerk’s mother Cathy, who is also his agent, revealed to BBC Radio Northampton last week that the high-profile move was unlikely to go ahead.

“I have a contract from 1 November 2007 to 30 June 2010 signed by Joe and chief executive Allan Robson,” she said.

“On 30 October we received an e-mail to say they would not honour the deal.”

Van Niekerk captained the national schools, under-19 and under-21 sides before winning the first of his 46 Springbok caps.

He was one of South Africa’s top players at the 2003 World Cup but missed the 2007 tournament because of a back problem.

So far van Niekerk has spent his whole playing career in South Africa, but he came to Franklin’s Gardens towards the end of last season and was clearly excited by what he saw, despite the team’s ultimately unsuccessful battle against relegation.

“To come to a club that’s as rich in tradition and history as Northampton is an awesome thing,” he said at the time.

“I could not believe the supporters when I came to watch the game, they were very passionate. I’m looking forward to it immensely.”

Van Niekerk now looks likely to join Super 14 side, the Lions.

England’s World Cup winning wing Ben Cohen has walked out on relegated Northampton Saints, following the appointment of Bruce Reihana as club captain.

Saints confirmed in a statement that the 56-cap veteran had spat the dummy and indicated his intention to leave the club because he did not get the captaincy.

The 28-year-old Cohen, who has played 270 games and won a Heineken Cup winners’ medal in 2000 in his 11-year Saints career, has failed to attend training at the club since the captaincy appointment was announced last Wednesday.

“In doing so he made himself unavailable for selection for [last] Sunday’s pre-season friendly against Samoa,” the club statement said.

With Saints’ opening match of the National League One season, against London Welsh, just over a week away and despite meetings and repeated requests from director of rugby Jim Mallinder and chairman Keith Barwell, Cohen has continued to stay away from training this week.

“Ben came to see me and said he was unhappy about not being appointed captain. He said: ‘That’s it, I’m off’,” explained Barwell.

“I am bitterly disappointed both with Ben’s decision and also with his action in staying away.

“He has been a brilliant servant to the club for more than 11 years, but no man is bigger than the club. It is the director of rugby’s responsibility to appoint the captain and I support Jim’s choice of Bruce Reihana wholeheartedly – his decision must be final.”

Mallinder added that they will not release Cohen and he may well sit on the sidelines for the season if he doesn’t play.

“Ben’s contract with the club runs until the end of the coming season and he is not able to play for any other club in the meantime.”

Cohen came from the junior club route of the Old Scouts, through the Saints youth system and onto World Cup-winning glory.

He made his Saints debut against Treorchy in the 1996/97 season and has rarely been left off the team sheet.

Cohen won his first cap for England against Ireland in the 2000 Six Nations and since then has added a further 55 caps to his tally. His score rate is just as impressive for his country and has racked up 29 tries.

But he lost form since 2004 and also lost his England spot.

He was also dropped from the Saints starting XV by former head coach Alan Solomons.