Pakistan squash legend Jahangir Khan is famed for winning 555 matches in a row, but a new book has cast doubt on the figure and says it might be much lower.

In “Jahangir Khan 555”, authors Rod Gilmour and Alan Thatcher say nobody was keeping proper records during Khan's five-and-a-half-year unbeaten run from 1981 to 1986.

Khan's streak of 555 is credited as the longest unbeaten run in any sport, but the authors say their research has convinced them the figure is “factually incorrect”.

“There were no statisticians at the time chronicling his matches and not once has the figure been highlighted in press reports of the time,” Gilmour said in a press release.

“We believe that it could be significantly lower. After all, he would have to have played over 20 world tour tournaments each year for five years, which at the time was certainly not the case in tour matches.”

However, Khan insisted the figure could be even higher than 555, as it doesn't take into account exhibition matches.

His winning streak from 1981 was finally brought to a halt by New Zealand's Ross Norman at the 1986 world championships in Toulouse.

“If you calculate it, it could be more. I played invitational, exhibition and challenge matches,” he was quoted as saying.

“The 555 figure should only be my tournament matches. But it could be between six to seven hundred matches if you include the others. Because I wasn't losing those either!”

Thatcher said if Khan didn't win 555 in a row, the longest winning streak would go to Dutch wheelchair tennis legend Esther Vergeer, who won 470 consecutive matches over 10 years until her retirement in 2013.

“His five-and-a-half-year unbeaten run is certainly not disputed. That will surely never be conquered,” Thatcher said.

“It's the final tally which we wanted to solve for accuracy's sake. The real figure? It's hard to say. But it could be lower than 500. “