London - Arsene Wenger insisted Arsenal were at fault if Alexis Sanchez had missed a routine drugs test on the same day as he was completing his transfer to Manchester United but insisted both the player and the Gunners had "nothing to hide".
Reports in the British media late on Thursday suggested the Chile forward had contravened the Football Association's 'whereabouts' rule by missing a doping test scheduled for Monday - the same day as a move to Premier League rivals United was being completed.
The 'whereabouts rule' in the Premier League gives players a responsibility to update their individual details.
The system aims at making it easier for anti-doping authorities to conduct tests.
Sanchez's 'whereabouts' changed on Monday when he moved to Manchester United, although it appears the Chile forward was still technically a registered player with London giants Arsenal when the possible infraction of anti-doping rules took place.
"It is just a bad day for him to be tested," Arsenal manager Wenger told reporters on Friday. "Honestly, on the administration side it would still be our responsibility because he had not moved.
"The most important is the intentions are right. The intention of Alexis was certainly not to hide, nor was our intention to hide anything. We have nothing to hide."
Wenger, Arsenal's manager since September 1996, added: "I pushed always for football to do more against doping, so I don't see why we should not co-operate.
"We try our best, but this was a special day. On Monday there was a lot going on, it is a special day for Alexis Sanchez - you have to do paperwork and travel.
"I think it is a special event for him to miss a drugs test because he was somewhere else," he said.
"I'm quite relaxed because we have nothing to hide here, we always try our best to co-operate with doping control. He has been tested so many times here that it's no worry for me that he has any doping problem."
Rules drawn up by England's Football Association (FA) state an individual player must inform the authorities if they are set to miss a scheduled training session.
That also means providing "notification (which) must include your name, your club, and an address and time where you will be available for at least one hour during the day you are absent."
Players or clubs who commit three 'whereabouts' violations within a 12-month period are at risk of disciplinary action.
Last year both Manchester City and Bournemouth were fined £35 000 after they each failed to provide accurate information for doping officials.
Premier League leaders City were interested in signing Sanchez before hearing of the Gunners' reported £35 million price tag and the player's wage demands.
That paved the way for United to clinch a straight swap deal that saw Henrikh Mkhitaryan join Arsenal.
Sanchez could make his United debut later Friday after being included in the squad selected by Jose Mourinho for the FA Cup fourth-round tie away to fourth-tier club Yeovil Town.