Dinamo Zagreb midfielder Arijan Ademi failed a drugs test following Arsenal's 2-1 defeat to the Croatian side in the Champions League last month.
The Gunners kicked off their European campaign with the shocking defeat in Zagreb before another disastrous result at home to Olympiakos left them on the brink of elimination heading into a double-header against Bayern Munich.
Ademi failed the doping test following the game on September 16, and will face disciplinary proceedings should his B-sample also return positive.
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But despite playing the full 90 minutes in their win over the Gunners, Zagreb will face no sanctions. There are no rules to deduct points or disqualify a team from European competition unless two or more players are found to have doped.
The Croatian champions released a statement, saying: "We are aware of the results of the doping control test after the match of the Champions League first round against Arsenal and that our player, Arijan Ademi, was positive, and that UEFA opened proceedings against him.
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"According to UEFA rules, Dinamo cannot comment on the case until the B sample is given. Our players have been regularly subjected to doping controls for years after European and league games and never has anything like this ever happened."
Here are some reactions from Arsenal fans:
The Gunners only have themselves to blame for their current predicament and will have to drastically improve if they are to keep their hopes of qualification from Group F alive.
Arsene Wenger's tactics in the competition have been nothing short of disastrous and their chances of picking up the necessary points against Bayern are slim at best.
The two clubs have a recent history in the Champions League and the Bavarian outfit have often come out on top.
They swept the Gunners aside in 2014, winning 3-1 on aggregate after a 2-0 win at the Emirates. They also progressed on away goals in 2013 after Arsenal produced a stunning performance, in vain, to win 2-0 at the Allianz Arena.
The north London club never make things easy for themselves, but this time it appears they have bitten off more than they can chew.
Can Arsenal beat Bayern Munich? Have your say in the comments section below!