Berlin: Bayern Munich head to Spain for Wednesday's Champions League semi-final -- and Pep Guardiola's return to Barcelona -- showing cracks in confidence following back-to-back defeats.

After wrapping up their 25th German league title last Sunday, Bayern's costly penalty shoot-out defeat to Borussia Dortmund last Tuesday in the German Cup semi-final was followed up by a 2-0 loss at Bayer Leverkusen on Saturday.

It has been the worst possible run-in to the match at Camp Nou where Guardiola will be making his first return to the club where he won 14 cups and titles in his four years in charge up to 2012.

‘We aren't going to talk ourselves into a corner, the season has been awesome until now,’ said Bayern's director of sport Matthias Sammer.

‘The players and coach have deserved every compliment that has come their way more than any criticism.’

But the Dortmund defeat brought injuries to two stars.

Arjen Robben limped off -- and out for the rest of the season -- after lasting just 16 minutes of the second-half.

Having recovered from torn abdominal muscles, the Dutch winger, who has 19 goals this season, tore his left calf to end his season.

Then Robert Lewandowski, Bayern's top scorer with 23 goals, fractured his nose and cheekbone in an extra-time clash with Dortmund goalkeeper Mitchell Langerak.

Sammer says the decision as to whether Lewandowski plays at Barcelona with a protective mask will be made by the player.

Guardiola gave reserve team defender Rico Strieder and striker Lukas Goertler senior debuts at Leverkusen while resting stars Thomas Mueller, Jerome Boateng, Juan Bernat and Xabi Alonso.

‘The main thing is that no one else got injured,’ admitted Germany captain Bastian Schweinsteiger as Bayern headed back to Munich.

While Bayern were struggling in Leverkusen, Barcelona ran riot at Cordoba with Luis Suarez claiming a hat-trick while Lionel Messi hit two and Neymar also netting in Saturday's 8-0 thrashing.

- No respect over 90 minutes –

‘With all due respect, Barcelona got that result against the bottom side,’ insisted Sammer.

‘We played with two youth team players against a Champions League side. There's a difference.

‘We have the necessary respect for Barcelona and their many world-class players, but we also have a few world champions.’

Bayern's Spain international Javi Martinez came off the bench to make his first appearance after nearly nine months out with injury. But it is probably too soon for him to face Suarez, Neymar and Messi.

Centre-back Medhi Benatia is set to feature in Barcelona after a leg injury.

‘I played against Suarez in the Europa League, when he played for Liverpool,’ said the 28-year-old.

‘I haven't played yet against Messi and Neymar, but there is always a first time for everything.

‘Personally, I respect them, but that's not valid for the 90 minutes on the pitch, there will be no respect then.’

This is not the first time Bayern have suffered a dip after winning the league title under Guardiola.

Having wrapped up the 2013-14 title with a record seven games to spare, Bayern suffered a rare league defeat at Augsburg which was followed by a 3-0 mauling in Munich by Dortmund.

Two weeks later, they lost 1-0 at Real Madrid in last year's Champions League semi-finals first leg before being routed 4-0 in Munich.

Sammer insists the new back-to-back defeats have had no impact on the squad, other than ending their hopes of winning the treble.

‘Pep has already won five titles with Bayern and his second season isn't over yet,’ said Sammer.

‘He shouldn't have to feel under too much pressure against his former club.

‘I hazard a guess that he has more composure than that.’