The manager level is something that had it's use in the old version of the game - there was still the option to take over a low level team that has been abandoned.

When taking over such a team you would retain all your whole managerial history and your manager levels but your Club would need to have it own level due to the League competition it has to participate in. Basically you couldn't boost up the level of the new Club, so there was a need for two different types of levels. (This feature is no longer available in the old version)

Club Level & Manager Level.

These days, only the Club level is what the game takes in to consideration when organizing the League competition groups.

Don't panic if you go against a Manager level 40+ or something like that - that is most likely an old Manager who took over an abandoned Club while the old version was still supported.

NOTE: The club level is that which dictates what amount of stars will be shown, because your club level is the same as the level of the League competition in which you participate. Better details here.