Pep Guardiola starts another UEFA Champions League campaign under pressure to deliver glory for Bayern Munich as his side travel to Piraeus to face Greek champions Olympiacos on Wednesday.

The continental heavyweights have made another flying start in the Bundesliga, winning all four of their opening league matches and scoring 15 goals in the process. 

But it is in Europe where the two-time Champions League winning head coach knows he must deliver if his tenure in Germany is to be considered a success.

Guardiola's first two seasons at the helm have seen painful semi-final exits to Real Madrid and Barcelona in Europe's elite club competition and the Catalan will need to go all the way this year's competition to silence his doubters.

"I believe it would not do the club harm if they would bring in another coach," the club's former midfielder Dietmar Hamann said ahead of the game.

"If I had to rate Guardiola from zero to 10, I would give him a five - so right in the middle. In the league they were champions, but in the Cup they have lost to Dortmund and in the Champions League they tried twice and failed. 

"I do not know if another coach like Van Gaal or Heynckes would be in office after such results. You can lose against Real Madrid or Barcelona but the way and the naivety [of the defeats], for me that was very upsetting.

"If he wants to successfully complete these three years, he has to bring the Champions League."

Following his last-gasp penalty in Bayern's controversial 2-1 win over Augsburg on Saturday, Thomas Muller has netted six goals in four league games for Bayern, who will take to the field without star wingers Arjen Robben and Franck Ribery but are otherwise in a reasonable state of fitness.

The two teams are Champions League regulars. Olympiacos are making their 17th appearance in the tournament, while Bayern have participated in 18 of the last 19 editions, yet this will be their first meeting with each other since the 1980-81 season.

Marco Silva's men are in typically strong domestic form. They have won all three of their league matches to start the new season and only conceded one goal.

As ever, the challenge will be converting that success to the European stage. Olympiacos have never progressed past the quarter-finals and it was back in 1999 when they last reached that stage.