Arsene Wenger blasted the refereeing in Arsenal's 2-0 loss to Braga as the Gunners had a strong penalty appeal dismissed and saw Emmanuel Eboue stretchered off injured.
Arsenal skipper Cesc Fabregas was also injured in the game and will miss his side's trip to Aston Villa in the Premier League on Saturday lunchtime.
The Gunners' failure to not even pick up a point in Braga means they are now locked on nine points with the Portuguese side in UEFA Champions League Group H.
Wenger was left aghast at the officiating a the Estadio Municipal, in particular after Carlos Vela was booked for diving when it seemed he had clearly been taken down in the box.
He told Sky Sports: "It was a disappointing result as we played against a team who played in their own half.
"I felt we had back luck as well. We were punished when Eboue was kicked off the park and we had a penalty turned down.
"I would like to see what the fifth the official is doing. It has been proved again tonight that it is absolutely useless this system.
"It was a difficult performance. We needed to be patient. We didn't create many chances.
"It was a difficult game against a team who used all the tricks to slow the game down.
"For us we needed not to make a mistake but unfortunately when we were down to 10 v 11 we were open at the back.
"We made a mistake and they took advantage of it. We did not communicate and that's where we were punished."
"But I am confident we will qualify."
Wenger also confirmed the hamstring injury sustained by Fabregas, with the skipper a surprise inclusion in the starting XI following his recent fitness concerns.
He said: "It is a hamstring injury. It is difficult to be predict how long he will be out for. It is on the other leg.
"He will be out for the weekend."
Of Eboue's problem, Wenger added: "He is out for a while because of the very bad tackle, which went unpunished. It is a knee medial ligament strain. It will be a few weeks."