Pep Guardiola said Tuesday it is "getting tougher" to win the Champions League as he targets a second consecutive treble with his all-conquering Manchester City team.

Defending champions City, unbeaten in 19 games in all competitions, take on Copenhagen in the second leg of their last-16 tie at the Etihad on Wednesday, with the cushion of a 3-1 lead.

They beat Manchester United on Sunday to move just one point behind Premier League leaders Liverpool and are through to the FA Cup quarter-finals, where they will face Newcastle.

But Guardiola played down talk of a repeat of last season's heroics at his pre-match press conference on Tuesday.

"It's better to be here having already won the Champions League but as I said it (the treble season) is finished," he said.

"The only target is to try to qualify tomorrow for the quarter-finals," he added. "We are far, far away, talking about these things.

"We didn't say last season until we won the final against United in the FA Cup, so we are at the beginning of March."

Guardiola, who also won the Champions League twice as Barcelona manager, in 2009 and 2011, said the bar had been raised in Europe's top club competition.

"It's getting better and tougher," he said. I had the feeling when I arrived at Barcelona in the first years 'OK we will arrive in the semi-finals".

"Now, to reach semi-finals is so difficult. The teams are better and managers are better. Everything is even more difficult than when I was a football player. But at the end the better teams always go through."

But he played down the notion that winning with City last season -- the club's first-ever Champions League crown -- was a bigger achievement than lifting the trophy with Barcelona.

"No, I would not say that, otherwise I undermine what we achieved in Barcelona," he said. "I would not like that, which was really good.

"I am not saying that 'That prize is better than the previous ones'. It's not. Every moment is every moment.

"What I think when I was at Barcelona or Bayern Munich, here, every title you win is different. It's not for granted.

"It's not because it's easy. Every step you do is so complicated... you have to be good in the right moments, mentally, physically and the skills and the game plan and many, many things, luck in the right moments."