City's lineup is out and there is a lot of rotation, especially in defence were Reis starts alongside Ake, however, some of the news boys are in the starting lineup, as both Cherki and Reijnders start. I am very certain that Pep would use this tournament, particularly this group stage fixtures against weaker sides to understand his players better, especially the new guys and try to get a pattern of play for next season.
Reis will be tested on whether he can take the main position as Manchester City's center back from Dias. Manchester City's formation for the time being is different from usual. It appears Pep Guardiola is using a 4-1-4-1 formation. One player placed above the center-back is Reijnders who is usually Rodri's position. There could be a change in formation later.
There is another possibility that a number of main players such as Haaland, Silva and other names are reserved because the team to be faced is Wydad Casablanca, a representative from Morocco.