"We did the hard bit to score before half time," he told ITV Sport. "We had control and got caught on the counter-attack and lost the point. We gave the ball away at the edge of the box and they're a very good side on the counter attack.
"We kept them really quiet but we conceded that chance and they scored. It's going to be tough. The toughest group in the Champions League and we're still capable of going through but we didn't deserve to lose the game.
"We played some really good stuff and we were unlucky to concede when I thought we were playing the better football."
Arsenal visit Crystal Palace in the Premier League on Saturday.