MANCHESTER, March 5 — 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.