The Brazilian winger ended his seven-year spell in north London earlier this month, completing a £60 million move to the Saudi Pro League club.
Casseb said Martinelli’s departure was viewed as the right decision by both player and club after Arsenal underwent a significant rebuild.
“Arsenal underwent a huge rebuilding process and last season they won the Premier League. We felt it was time for him to move on and the club saw it the same way,” Casseb told Itatiaia Esporte.
The 25-year-old made 278 appearances for Arsenal after joining from Ituano in 2019, scoring 62 goals and providing 36 assists.
Casseb also confirmed that Martinelli had opportunities to remain in Europe before choosing Al-Hilal.
“Did he get offers? Yes, he did. We had offers from Italian clubs, German clubs and other Premier League clubs,” he said.
“But it was a moment when I think he needed, and also wanted, to clear his head a little and change his environment.”
Martinelli’s transfer became Arsenal’s record sale, according to his representative, while the winger has now joined an Al-Hilal squad that includes several high-profile internationals.
Casseb said the Saudi club’s ambitions also played a role in the decision, describing its recruitment strategy as part of a wider attempt to attract younger players to the league.
Martinelli therefore had the option of remaining in European football but opted for a new challenge in Saudi Arabia.