BERLIN (AFP) - Pep Guardiola has insisted his Bayern Munich side must improve ahead of Wednesday's Champions League clash at Manchester City after stuttering to a 1-0 win over VfL Wolfsburg.

Despite enjoying their customary 70 per cent ball possession at Munich's Allianz Arena, Bayern needed more than an hour to break down the Wolves defence on Saturday to stay second in the Bundesliga.

Manchester City warmed-up for the visit of the European champions with a 3-2 defeat at Aston Villa to leave Manuel Pellegrini's side fifth in the Premier League, but Guardiola said Bayern must tighten up.

"We won, but we must improve a lot of things," admitted the Spaniard ahead of the trip to England and next Saturday's Bundesliga clash at third-placed Bayer Leverkusen.

"We had a few problems in the second half which we need to solve. I am certain that we will put in a good performance in Manchester and at Leverkusen."

Bayern and City are battling for top spot in Group D after winning their opening matches with Munich seeing off CSKA Moscow 3-0 at home and City winning 3-0 at Viktoria Pilsen.

But against a dogged Wolfsburg defence Bayern's finishing and passing let them down in a below-par performance.

Guardiola took off Arjen Robben, Bastian Schweinsteiger and Mario Mandzukic in the second-half with one eye on the trip to England, but Bayern were far from impressive.

They only created 11 shots on goal all game and too many sloppy passes allowed Wolfsburg to contain the European champions for the majority of the match.

Germany midfielder Thomas Mueller scored the winner with his first Bundesliga goal of the season when he met Franck Ribery's pass from the left wing at the far post on 63 minutes.