The four-time Grand Slam champion had already cast doubt over his participation with comments he made when asked about the team competition at the China Open last month.
"The truth is that I havenât decided whether or not to play the Davis Cup, I'll make a choice later," the 24-year-old told reporters.
"I can't give an answer right now. I'm only focused on the next tournaments I'll be taking part in."
Volandri has now revealed that Sinner has chosen not to compete at the Davis Cup Finals this year as he confirmed Italy's squad for the event.
"Sinner has not given his availability for 2025," the former ATP player said.
"The Davis Cup is, and will always remain, his home and I am sure that Jannik will soon return to be part of the team."
Italy's five man squad features Lorenzo Musetti, Matteo Berrettini, Flavio Cobolli, Andrea Vavassori and Simone Bolelli.
Sinner led Italy to win the previous two editions of the Davis Cup Finals, which were held in Malaga.
Angelo Binaghi, the president of the Italian Tennis Federation, said: "We understand and respect Jannik's decision, which is very painful for us.
"(It) comes at the end of a long and intense season, in which he once again demonstrated that he is an extraordinary point of reference for the entire Italian tennis movement."
The world No 2 is in action at the ATP 500 tournament in Vienna this week, where he will face 51st-ranked Daniel Altmaier in his opening match.