2. Inability to play with a suitable formation:
Bayern used a play a 4-3-3 a few years ago with Robben and Ribery as the two wingers and Robert Lewandowski as the striker. Ribery has played in 403 matches for Bayern and scored 117 goals and Robben has scored 141 from 304.
Age has caught up with both of them, but, surprisingly, Bayern still continue to play a 4-3-3 or 4-2-3-1 in most of the matches. Robben has been having frequent injury problems for quite a while now and Ribery is 35 years old. Therefore, Bayern would have to stop depending too much on them and give chance to younger players.
Youngsters Serge Gnabry and Leon Goretzka can be played in the starting eleven as wingers or side-midfielders. Gnabry is a very fast and skilful player and could actually become an asset for Bayern in future.
Goretzka is strong defensively and can fall back easily while playing as a side-midfielder. Bayern can think of playing a 4-4-1-1 formation with Ribery and Gnabry as the side-midfielders and Thomas Muller as the support striker behind Robert Lewandowski.
Goretzka can be used as a substitute and Robben can play when fully fit. They have side-midfielders and fullbacks capable of playing frequent crosses to the box and therefore, this formation might suit them. Bayern would actually love to have players like Ivan Perisic or Leroy Sane on the flanks, but signing those players is not going to be easy.