When a sportswear company pays you £4m to wear their logo, it only seems reasonable to oblige.

But Scots tennis star Andy Murray has come under fire for displaying a rival manufacturer's apparel in front of a TV audience of millions.

Last night marketing gurus described his choice of attire - a Lacoste hooded top - as he watched his brother Jamie's mixed doubles championship win on Sunday as "unprofessional" and "disloyal" after he signed an exclusive multi-million pound sponsorship deal with Fred Perry last year. Murray, who missed this year's Wimbledon tournament because of a wrist injury, was seen by a huge TV audience and pictured in the newspapers cheering on his brother and doubles partner Jelena Jankovic.

The Perry laurel garland logo only got a look-in when Murray took off his top towards the end of the coverage, but the Lacoste logo also featured on Murray's website earlier in the week, fuelling accusations of betrayal.

Nigel Currie of London-based Brand Rapport said: "Andy Murray's exclusive deal with Fred Perry is one of the biggest endorsements in British sport and they are entitled to feel let down by this mistake," he said. "I suspect it was probably borne out of naivete, but the rules are pretty clear and a high-class professional sportsman would be expected to be dressed in the correct apparel in all appropriate situations."

Mr Currie, who is chairman of the European Sponsorship Association, added: "Lacoste must be chuckling to themselves at the free publicity and the obvious discomfort of one of their main rivals in the tennis and fashion sportswear sector."

Richard Martin, marketing director of Fred Perry claimed the issue was a "mountain out of a molehill". But he added: "How the matter will be dealt with will be down to someone else in the company."

Rather more ominously Hamish Pringle, director general of the Institute of Practitioners and author of the book Celebrity Sells, said: "The case of a celebrity being disloyal to the brand is a pretty straightforward one to deal with, assuming the contract is correctly drawn up."

Murray's manager, Patricio Apey of Ace Group, did not return calls yesterday but said recently: "Andy certainly has a rebel streak, but he also has a head on his shoulders."