Shares in Umbro have fallen 4% after the sportswear firm lost its contract to make Chelsea Football Club kits.
Umbro has deals with more than 150 teams
Chelsea said the Umbro deal, which gives the firm the lucrative right to make replica shirts, would end five years early by mutual agreement.
The contract will expire in June 2006 instead of 2011 - with the club making a £24.5m ($45.7m) payment to Umbro.
The UK sportswear company said it now expects pre-tax profits to fall by £1-£2m this year.
Umbro had paid the current Premiership leaders for the right to make its kit and reaped hefty profits from manufacturing replica shirts for fans.
Neither Chelsea nor Umbro said why the contract was ending.
"We believe this represents a good deal for shareholders," Umbro chief executive Peter McGuigan said in a statement.
Premiership kit deals
Manchester United: Nike
Manchester City: Reebok
Aston Villa: Hummel
"It provides us with a material cash injection in the summer of 2006, which will fuel a higher level of global investment in the brand over the medium term."
Chelsea chief executive Peter Kenyon said the club believed the decision would "help us achieve our strategic long term goals in the future".
The end of the contract will fuel speculation that Chelsea is lining up a deal with either Nike or Adidas, the world's top sportswear companies.
Mr Kenyon has been trying to turn the club into a powerful international brand since his arrival from Manchester United, where he brokered a record-breaking £303m marketing arrangement with Nike.
Shares in Umbro, which will remain kit sponsor during Chelsea's 2005-6 centenary season, closed down 4.5 pence at 105p.
In 2004, sales of Chelsea products were worth £8.2m, accounting for 6.1% of Umbro's UK turnover.
The company will bring out unique Chelsea products for the centenary celebrations but expects sales to fall this year.
"When fans know the shirts are changing, they tend to sell less well," a spokesman for Umbro said.
"In this case, the deal with the current Chelsea shirt sponsor, Emirates, is also coming to an end."
Cheshire-based Umbro makes kit for 150 teams worldwide, including the England national squad.
Profits in the half-year to July 2004 were £16.55m, a 51% increase on the same period in 2003.