A judge ruled the company should have been given the chance to match a shirt deal struck with Elite/Hummel.
Rangers terminated a merchandise agreement with Sports Direct last year, but the firm should have been given the chance to compete with new offers.
The club said it would “meet any financial award made by the court”.
Judge Lionel Persey QC ruled that the new deal with Elite/Hummel, thought to be worth £10m, breached the agreement which said Sports Direct was to be given the chance to compete with new offers.
The judge also threw out Rangers’ request for any payment to Mike Ashley’s company to be limited to £1m.
As part of the judgement, there was stinging criticism aimed at Rangers secretary James Blair who was accused of being “unconvincing” in his evidence and “untruthful” in his dealings at the time.
The judge said: “The consequence of my findings is that Rangers was in breach of its obligations.
“I am satisfied that SDIR (Sports Direct) was not only entitled to match the rights offered to Hummel/Elite but would have done so.
“Those rights were not only not offered to them but Rangers, through Mr Blair, untruthfully asserted that Hummel had not been granted any Offered Rights and did not provide SDIR with a copy of the Elite/Hummel agreement.”
He went on to say that, as such, Sports Directs losses were likely “to be in the order of many millions of pounds.”
Sports Direct has now been granted an injunction to the latest deal – an injunction that Rangers argued would see them lose significant revenue, be open to legal action from Elite and even impair its ability to function as a football club.
Mike Ashley, who was a former Rangers shareholder, struck a deal with a previous board that saw his company take in around 93p from every £1 made from the sale of strips and merchandise.
That deal led to some fans boycotting Sports Direct stores and their sale of Rangers kit.
The amount of money now due to Sports Direct is still to be determined but Rangers are understood to be appealing against the latest ruling.
A statement posted on the club’s website read: “Rangers would like to reassure supporters that matters concerning the litigation currently being brought against it by SDI Retail Services Limited are not as reported.
“Rangers was disappointed by the terms of the recent court judgment but respects the decision of the court and will meet any financial award made by the court.
“No such award has yet been decided and at this stage Rangers does not even know how much will be sought. Contrary to some reports, the judge has not determined that the contractual cap on damages will not apply.
“Rangers would also like to reassure supporters that no steps have been taken to stop supporters being able to buy this season’s replica kits.”