JJB shares lost a fifth of their value on Wednesday after one of its biggest shareholders wrote off its investment in the struggling sports retails with an impairment charge. US-based Dick's Sporting Goods, which only made its £20m investment five months ago, blamed its decision on the company's on-going under-performance.Chief Executive Edward Stack said: "JJB's performance has materially deteriorated from its expectations, partly due to a worsening macro environment in Europe, adverse weather conditions in the first quarter and lacklustre sales associated with the recent Euro Championships."While we continue to believe in the underlying opportunity within the UK sporting goods market, in light of these developments and our own assessments, we have determined to fully impair the value of our investment. As we indicated at the outset, this is a high risk investment that was structured to provide us with meaningful upside and capped downside."We have no further funding obligations to JJB at this time and will continue to monitor the situation."The firm took a $32.4m impairment charge that has, in effect, written off the investment. Just last month JJB's Chief Executive Keith Jones announced his resignation following the group's poor sales. On Tuesday Sky reported that Jon Moulton, a veteran of private equity, is looking to takeover the sports merchandiser. JJB shares were down 21.39% to 3.40p by 16:48.NR