The chairman and chief executive of Maria Sharapova's racket sponsor has questioned the decision by the World Anti-Doping Agency to add meldonium to its list of banned substances in January.

Johan Eliasch, the boss of sportswear manufacturers Head, said WADA should have continued to allow some usage of the drug on medical grounds as he reiterated his company's strong support for the Russian superstar, who is facing the prospect of a lengthy ban after testing positive for meldonium at the Australian Open.

Sharapova stated this week she had been taking it for a number of minor health complaints, and missed an e-mail informing her that it had been added to the list of prohibited substances in the new year.

Despite a number of her sponsors, including Nike and Porsche, distancing themselves from Sharapova, Head issued a bullish statement on Thursday offering the player its full support and a contract extension.

And Eliasch went a step further on Friday with a second, strongly-worded statement in which he denied any "evidence or intent" by the player to gain a competitive advantage by using meldonium.

Citing Sharapova's issues with flu-like symptoms and diabetes, Eliasch said: "Although it is beyond doubt that she tested positive for a WADA-banned substance, the circumstantial evidence is equally beyond doubt that the continued use of meldonium after January 1, 2016 in the doses she had been recommended, which were significantly short of performance-enhancing levels, was a manifest error by Maria.

"In the absence of any evidence of any intent by Maria of enhancing her performance or trying to gain an unfair advantage through the use of [meldonium], we further conclude that this falls into the category of 'honest' mistakes.

"Furthermore, we question WADA1s decision to add meldonium to its banned substances list in the manner it did; we believe the correct action by WADA would have been to impose a dosage limitation only. In the circumstances we would encourage WADA to release scientific studies which validates their claim that meldonium should be a banned substance.

"The honesty and courage she displayed in announcing and acknowledging her mistake was admirable. Head is proud to stand behind Maria, now and into the future and we intend to extend her contract.

"Maria may have made a mistake, but she has earned the benefit of the doubt and we are extending it to her. We look forward to many more years of working with Maria."

Head's stance has already been questioned by Andy Murray, who is also sponsored by the company.

At a press conference at Indian Wells on Thursday, Murray described Head's initial stance as "strange", adding: "I think at this stage it's important really to get hold of the facts and let things play out, like more information coming out before making a decision to extend the contract like that, in my view. I personally wouldn't have responded like that."