Eliaquim Mangala believes Manchester City will continue to be punished for lapses of concentration in Champions League matches, unless they can learn to maintain focus for the entire 90 minutes.

City were defeated 2-1 by Juventus in their opening Champions League fixture on Tuesday and Mangala believes the Premier League leaders learned some valuable lessons from the contest.

The French international said his teammates must learn that any momentary loss of focus that might go unpunished in the Premier League can have potentially dire consequences in European competition.

"The Champions League is decided on small margins, on one or two balls," said the centre-back," Mangala said post match.

"We were controlling the game, and then on those two balls we conceded twice. At this level, you can't concede goals like that.

"They have a quality team, and we paid for [our mistakes] right away.

"It's obvious that we didn't do well, but it's not over, there are some games left. So we must refocus. But in the Champions League, we shouldn't be as relaxed as we were in those kind of situations.

"In the Premier League, you're allowed a bit more... I won't say mistakes... but you can have some moments when you are a bit less focused. That is not possible in the Champions League."