Monaco star Mbappe, 18, is reportedly nearing a surprise switch to PSG, who have already added Neymar to their squad during the transfer window.
The teenager's departure, and to a rival, would be the latest blow to Ligue 1 champions Monaco, who have seen the likes of Bernardo Silva, Tiemoue Bakayoko and Benjamin Mendy depart.
While the signing of Mbappe would make PSG even hotter favourites to claim the title, Ranieri said the move could be a good one for the league.
"Yes it's good. The championship can grow, Paris can grow," the Nantes coach said on Thursday.
"The idea is to win the Champions League. It's normal. It's normal."
PSG had won four consecutive league titles before Monaco claimed their first since 2000 last season.
While he denied Unai Emery's men were certainties, Ranieri admits PSG are very likely to again be crowned champions.
"Sure? We are only sure of death," the Italian said.
"But Paris will win, 90 per cent [chance]."