The Borussia Dortmund shot-stopper is infuriated by the dropped points at Signal Iduna Park, but conceded that his side were not determined or clinical enough to win
Dortmund were dominant for large periods, but Aaron Ramsey struck the only goal of the game as the Gunners claimed revenge for their 2-1 home defeat to Jurgen Klopp's men on matchday three.
Weidenfeller, 33, was disappointed that his team-mates were unable to take advantage of their superiority, but conceded that they lacked the determination and enthusiasm needed to claim a win.
"It is a little bit of an injustice," he told ZDF. "But we had that bit of luck in London and today we were punished.
"We settled into the match immediately and had great opportunities. But we lacked determination in the decisive moments.
"We were not energetic enough and always tried to play nicely and maybe do another pass and another pass after that.
"We gave away big points. Group F is totally open now. We have to win against Napoli and best thing would be to win by two goals."
Dortmund coach Klopp remained adamant that last season's Champions League runners-up can make it out of the group stage this campaign but lamented his players' profligacy against the Gunners.
"I told the team in the dressing room what everybody saw: we were not rewarded for our efforts," he said. "But nothing has come of the game.
"Of course, this was not planned. The way it is now, the group will be thrilling for a longer time. We still have every chance. If we win our two games, all should be good. Of course, for now, it feels bad.
"We simply did not convert our chances. Arsenal scored with their first shot during a phase where we were playing pretty good.
"We did not turn our good chances into guaranteed goals. We did many things right, but, in the end, we were not focused enough and not clinical enough."
Klopp also hinted that some decisions by official Bjorn Kuipers may have went against his side.
He added: "The referee will not get the reputation of being a referee that favours the home team after tonight. But the analysis starts with looking at your own mistakes."