Mbappe joined PSG from AS Monaco in the latter stages of the summer transfer window, while Dembele was also on the move as the 20-year-old swapped Borussia Dortmund for Barcelona.
Mbappe and Dembele are considered to be two of the brightest talents in the French national team, and the former has backed his international teammate to 'reach another level' playing alongside Lionel Messi and Luis Suarez.
"I told him not to think twice because it is a great opportunity for him. He can become a better player playing alongside Lionel Messi and Luis Suarez. He already has incredible talent, but he can make another step up," Mbappe told The Telegraph.
Mbappe and Dembele are both expected to make their debuts for their respective clubs this weekend.