Monday 14 March 2016 14:28, UK
Per Mertesacker believes Arsenal need to rediscover their killer instinct after they crashed out of the FA Cup on Sunday.
Second-half goals from Odion Ighalo and Adlene Guedioura earned Watford a 2-1 victory at the Emirates to inflict a first defeat in the competition on the Gunners for more than three years.
Arsenal face a daunting task on Wednesday in a bid to reach the quarter-finals of the Champions League as they travel to the Nou Camp attempting to overturn a 2-0 deficit against a Barcelona side looking to stretch their unbeaten run to 38 games.
"It is as you can imagine, we are out of the competition and the treble dream is over, that is the conclusion of Sunday's game," said Mertesacker.
"The season is not over. We play in a confident way, we maybe lack that bit at the end. What is really important in football, to be successful we need to score. The desire to play together and to be good at a team is there, you can feel that, even if there is a bit of negativity I can understand."
The Arsenal captain was left frustrated at the amount of chances missed late in the game and believes a lack of confidence is costing his side in front of goal.
"It looks like we play, and play and play until the opposing team scores," Mertesacker added. "That is something we need to work on. We had the opportunities and the possibilities when they were 2-0 up to come back and we kept going.
"You have to give credit because we kept going and created chance after chance, but at the moment we lack that killer instinct. We need to work on that if we want to be successful in the Premier League and the Champions League."
