By James Davey

LONDON (Reuters) - Struggling British sportswear retailer JJB Sports was dealt a further blow with David Jones, chairman and architect of its rescue, stepping down to continue his long-running battle against Parkinson's Disease.

The firm said on Thursday 28 January that Jones, a former chief executive of fashion retailer Next who has suffered from the debilitating neurodegenerative disease since 1982, will step down as chairman on January 31 but will remain a non-executive director.

The news came as JJB, which saw suppliers hold back stock as it battled to avoid administration last year, posted further falls in sales and gross margins, albeit at a slower rate.

Shares in JJB Sports, which have fallen 27 percent in the last three months, were down 4.7 percent at 20.25 pence at 9:30 a.m., valuing the business at about 133 million pounds.

Last year, as JJB teetered on the brink of administration, Jones steered the firm through the 83 million pounds sale of its fitness clubs, a debt restructuring with creditors and a 100 million pound capital raising.

John Clare, the former CEO of electricals retailer DSG International and JJB's senior independent director, will be acting chairman until a permanent appointment is made.

Last month JJB poached DSG's retail director, Keith Jones, to be its new CEO. However, he does not start until March 1.

JJB said sales at stores open over a year fell 21 percent in the three weeks to January 24, taking the cumulative fall for the 52 weeks to January 24 to 37 percent. Total sales slumped 51 percent.

The firm said its second-half gross margin of 40.4 percent was 260 basis points lower than the comparative period last year, but 6.4 percent better than the first half.

With its stock position "steadily improving," it was on target to be fully stocked by April 2010, in time for Easter and the soccer World Cup.

"Taking sales and margins together ... this is a slightly disappointing update and will result in higher losses than broadly envisaged," said Matthew McEachran, analyst at Singer Capital Markets.

He is forecasting a full-year to end-January 2010 pretax loss of 64.8 million pounds, which compares with a forecast consensus loss of 53 million pounds, according to Thomson Reuters I/B/E/S.

JJB has also appointed two new non-executive directors -- David Adams, the former deputy chief executive of House of Fraser, and Matthew Pinsent, the quadruple Olympic gold medallist in rowing who is now a broadcaster and journalist.

(Editing by Julie Crust and Jon Loades-Carter)