Mandelli said: "I can't believe I've been called into the senior team," he said.
"I know I've played two good games against England and France with the A team and that coach Franco Bernini said to me he was very pleased.
"But I never heard of the interest of (Italy coach) John Kirwan, to be honest.
"I haven't spoke with the coach yet and also after this call up I'm still feel I am the 26th player in the squad.
"I have only just arrived here so I most keep patient."
Despite his surprise, Mandelli insists he is ready to make the leap to international rugby.
"If I have the opportunity to show I much I'm worth against the Scottish or on any others occasion I will make sure I will be ready for it," he vowed.
"But in my position there is Aaron Persico who is very good and I do not want compare myself to him, he can play anywhere and defend so well.
"I'm a flanker but in my point of view I'm more attacking than Aaron Persico and more defensive than Andrea De Rossi although I can also play at number 8.
"The only thing that matters is a victory for Italy."