This suggestion is interesting. I like having this feature. I just wonder if there will be teams which fully concentrate on private league and ignore all official matches.

Some teams may use their 11 better players to play private league. Conditions of these players will not decrease. So they may even play many matches on same day.

For official matches, they will use their 11 worse players. If they do not concern official competitions, they may not care the results and condition/morale loss of those 11 worse players. Low legue ranking may even help them keeping the star of the players for association matches. The only problem is injuries. They may still need to use red packs to heal injured 'worse' players so that they need not to use 'best' players in official matches.