Johnsrud Sundby's failure to declare his use of a nebulizer on the advice of team doctor Knut Gabrielsen breached World Anti-Doping Agency (WADA) rules, and sport's highest court CAS handed the 31-year-old a two-month ban effective from July 11.
"The Court of Arbitration for Sport (CAS) has concluded that Martin Johnsrud Sundby has violated the WADA rules through wrongful use of the legal asthma drug Ventoline," the Norwegian Ski Federation (NSF) said in a statement on Wednesday.
"The NSF assumes full responsibility in the matter, as the federation was of the opinion that it was not necessary to apply for a therapeutic use exemption (TUE)."
The dispute centred on dosage levels and the use of a nebulizer to administer the asthma medicine to the 31-year-old, who has suffered from the condition since childhood.
Cleared of any wrongdoing after an investigation by the International Ski Federation (FIS), WADA appealed to CAS, who accepted that Johnsrud Sundby did not intend to cheat but still found him to be in breach of the regulations.
"The results of two races during the season of 2014/2015 are disqualified. Consequently, Mr Johnsrud Sundby will be deprived of the victories of Tour de Ski and World Cup for the season of 2014/2015," the NFS statement added.
"The situation in which I find myself, is an athlete's worst nightmare. I have always competed on clean and honest terms," Sundby said in a statement. "I hope and believe that this case will not have major consequences for my future career."
(Reporting by Philip O'Connor in Stockholm; editing by Ken Ferris)
