The transfer window is still open, and because both coaches are experienced, they will know whether or not to sign fresh players for the following season after selling some of them to other clubs. Teams who sell players do so due of the manager's decision; if those players cannot fit into the pattern of football they want to play, they easily release them and use the ones that are available, or better yet, look for better replacements for them. If they've been doing well even after selling some players, they should be able to do the same when the regular season begins.
When the transfer window is still wide open like today, big clubs will consider players by looking at their games in friendly matches, but unfortunately, good players will have quite an expensive value, and that must be an important consideration for a team when they want to buy new players because, presently, not all teams have a large amount of money.