A number of players from France's Ligue 1 have made their way to the Premier League this summer which leads Mourinho to believe that his Blues will have to step up even more after their title win last term.
Clubs like Crystal Palace, Newcastle United and even Bournemouth have attracted quality players from France, as well as Holland, indicating to Mourinho that the teams in the lower part of the Premier League table are strengthening with real quality.
"Years ago, the best players at the best teams in other countries left to come to the big clubs in England," he said.
"[Now] in France, they are saying that French football is losing players even to medium-sized English clubs. This is the reality.
"Every club has very good players so it's difficult for the top teams in England because of the competitive nature, and because they have players who could play in our teams. (Yohan) Cabaye could play for Chelsea, (Georginio) Wijnaldum could play for Chelsea, (Max) Gradel could play for Chelsea – what's the doubt?"