Rule number one before playing Diego Simeone's Atletico Madrid side is not to make them angry...

But Arsenal infuriated their Champions League opponents ahead of Tuesday night's showdown at the Emirates and the visitors have made an official complaint to UEFA.

Atletico trained at the stadium on Monday afternoon but after working up a sweat on the turf, were unable to use their showers in the dressing room as there was no hot water. 

It had rained during the session so Atletico opted to get on their team bus in dirty kit before travelling back to shower at the team hotel. 

Atletico informed their hosts about the situation shortly after 5:30pm upon arrival but Arsenal were unable to fix it before Simeone and his squad left. 

The Gunners managed to have the hot water working again by the time Atletico were scheduled to finish training but the Argentine boss called time on it early. 

Given the outstanding facilities at the Emirates, Atletico were furious at the situation and even went as far as filing an official complaint to UEFA. 

The hot water was not working for either dressing room, though clearly it was not an issue for the home side with Atletico the only team at the ground. 

Arsenal have apologised to Tuesday night's opponents for the inconvenience. 

Under the official rules set out by UEFA, teams must provide hot showers but that is limited to matchdays and the infrastructure regulations do not extend to training sessions so it seems unlikely that the north London club will be punished. 

Arteta's men will be wary of any added motivation given to the visitors, who often use Simeone's siege mentality as fuel.

But the Gunners have won both of their games in the Champions League league stage so far and sit comfortably joint-top, fifth on goal difference. 

Atletico, meanwhile, are 10th having beaten Eintracht Frankfurt and lost a thriller against Liverpool at Anfield.   

Despite the anger from Atletico at Arsenal on Monday, Arteta had earlier spoken in glowing terms of his opposite number. 

'Well, obviously there is someone that I look up to and learn from him in many situations and what is for me outstanding is his passion,' he said.  

'I think for how long he's been in the game and in the same club with the same players, how you still have that hand and that capacity to transmit such an energy and willingness to win.

'It's a very tough environment that we live in and to keep convincing players you have to be extraordinary as well.

'I don't know [him] personally but everything I heard about him is that he's so good at doing that. That's one of the reasons why you are able to sustain at that level.'

'If he works in the Champions League, which is the highest competition in Europe, he can do it anywhere,' the Arsenal boss said.

'You have to come here and try it and feel it, but I'm very sure that his know-how is unbelievable, and his character and willingness will take him anywhere.'

And it is the defensive side of Atletico's play that impresses Arteta most, with the 43-year-old adding: 'First of all the willingness to win, you can sense that in every single ball, in every single yard, the way they play," Arteta said.

'So it's about how they compete and then after how they play.

'The level of organisation is really high, the level of discipline is really high, and then they have acquired a lot of talent throughout the years that are very specific for the needs and the way they want to play, and they are very good at exploiting those opportunities.'