The Colombia shot-stopper is on the verge of completing a transfer from the Ligue 1 club to the Emirates Stadium, after starring for his country at this year's World Cup.
On Saturday, Arsenal boss Arsene Wenger revealed that a deal had been agreed for the 25-year-old, with the player's arrival due to be announced officially over the coming days.
And Puel feels that the Premier League club are gaining a "very important" player.
Speaking to Sky Sports News, he said: "It is confirmed, yes. Ospina is a very important goalkeeper for us but Arsenal is fantastic for him."
When asked about the size of the fee, Puel played his cards close to his chest, adding: "It is a secret but it is a lot because he is a very good player."
With an official announcement from both club's now expected to follow, Ospina will look to begin the next chapter of his career.
However, Wenger has already indicated that he will likely have to wait for his opportunity to shine, with current first choice Wojciech Szczesny in line to start the new season between the posts.
"You know at the start Szczesny will be the number one, then again we'll be down to performances and, if Ospina shows that he is better, he will play," Wenger told ESPN.
Ospina made 29 Ligue 1 appearances last term as Nice finished just two points above the relegation zone before going on to impress in Colombia's run to the quarter-finals at the World Cup in Brazil.
