Harry Maguire and Jamie Vardy returned late for pre-season training after representing England, while Kasper Schmeichel, Ricardo Pereira and Shinji Okazaki also represented their respective nations in the knockout stages.
Manchester City's Kevin De Bruyne - who featured for Belgium - sustained what appears to be a serious knee injury on Wednesday, and Puel has suggested that the incident should serve as a warning during the early weeks of the campaign.
At a press conference, Puel told reporters: "It is important to see this. To analyse their rest. We can see what happens with De Bruyne for example. When an international player does not have a rest, it is a danger. Maybe later in the season.
"We need to a good focus about the game-time for the future. We have to protect the player. If you use players early, you need to be careful."
Schmeichel, Pereira and Maguire all started against Manchester United last week, while Vardy was introduced from the bench.