Naser escaped a two-year ban, which would have kept her out of the rearranged Tokyo 2020 Olympic Games, after a drugs tester knocked on the door of a storage cupboard instead of her apartment.

The 22-year-old, born in Nigeria but who runs for Bahrain, had been charged with four alleged whereabouts failures by the AIU in June.

This included a filing failure on March 16, 2019 and three missed tests on March 12 and April 12 of last year and January 24 of this year.

Missing three tests within 12 months is the equivalent of a doping failure and Naser had been provisionally banned after the charges were brought.

The World Athletics Disciplinary Tribunal ruled the alleged violation in April 2019 should not stand, however, which meant Naser had not missed three tests inside the 12-month window.

Filing failures are backdated to the first day of every quarter, so in Naser's case January 1, 2019.

The AIU has now confirmed an appeal to CAS.

"The AIU has submitted an appeal to the CAS against the Disciplinary Tribunal's decision to dismiss the charges against Salwa Eid Naser for whereabouts failures," an AIU statement read.

The Disciplinary Tribunal had acknowledged the decision in the athlete's favour was "borderline".

The Tribunal report claimed the circumstances "would have been comical were the consequences not so serious" with regards to the April case.

Doping control officer Enrique Martinez was looking for Flat 11 in Naser's building and found two doors close to one another.

The left hand door had the number 11 at its side and the right hand door had the number 954 and an intercom, with the number 12 underneath.

This caused confusion as the numbers 11 and 12 actually referred to car parking spaces and were not apartment numbers.

Naser's apartment 11 was behind the right hand door marked 954, and the left hand door marked 11 was a storage unit containing nothing but gas cannisters.

Martinez knocked every five minutes on the storage unit door before the required period of an hour had elapsed, unsurprisingly receiving no response.

He did not use the intercom on the other door, although the Tribunal heard that this did not work anyway.

However, he also did not try to open the second door, which Naser said would have been unlocked as a result of the intercom being broken.

"He should have opened the door to building 954 and knocked on the door of Flat 11 inside the building," the Tribunal report said.

"Had he done that he would have successfully located the athlete at her flat."

Martinez did try to phone Naser, but the Tribunal heard her details were not up to date and there was no number which worked.

The Tribunal deemed that Martinez should not be blamed, saying the door numbering is "extremely confusing" and that he "went beyond the call of duty" in attempting to find Naser later in the day and at the national stadium.

He had earlier been given a building number which did not exist, but found the correct place as he had a picture from a previous visit.

The report also concluded that Naser "did not help herself" in many regards due to the lack of information she had submitted.

The sprinter had reportedly changed her number several times and had struggled with the ADAMS system which athletes use to enter whereabouts details and other information, so they can be drug-tested at random.

The Bahrain Athletics Association had reportedly assigned a member of staff to input whereabouts information on her behalf.

Naser ran the third quickest 400m time in history, 48.14sec, on her way to gold at the Doha World Athletics Championships last year.

The "wonder time" was the fastest seen since East German Marita Koch set the world record of 47.60 in 1985.

Naser is also a double Asian Games gold medallist and a four-time Asian champion.

In June she had protested her innocence, saying she had "never been a cheat".

World Anti-Doping Agency President Witold Bańka said last month that he was concerned regarding the outcome of the case, adding that the organisation would consider an appeal.