Last week FIFA and UEFA issued a joint statement warning that anyone who played in a breakaway league would be banned from international competitions like the World Cup.
The response came after the circulation of a leaked document for a new league, to replace UEFA's Champions League, featuring 15 of Europe's biggest clubs as permanent members.
Radrizzani, who was strongly critical of the 'Project Big Picture' attempt by the 'Big Six' clubs in the Premier League to secure more power and greater resources, said the competition must be defended.
"I think the Premier League did a fantastic and wonderful job in the way that they have been creating value for this league and becoming the best league in the world. I think all the clubs and the entire domestic football need to defend and to preserve this value," he said when asked about the Super League.
Radrizzani, who said he aims to get Leeds back into Europe as part of his growth plans, announced on Monday that the National Football League's San Francisco 49ers, had increased their ownership stake in the club from 22% to 37%, with American Paraag Marathe becoming vice-chairman.
But while the Italian hopes to enjoy some "European nights" at a redeveloped Elland Road in the future, he said the game should not lose sight of the importance of national-level competition.
"The domestic league has a value that is extremely important because it is what generates resources for all the football pyramid. All of professional football benefits from the value of the top league.
"We need to be very careful to not damage something that became so important and the most recognised league in this world," he said.
The threat of a breakaway is being taken seriously by UEFA, which organises the existing European club competitions, including the flagship Champions League.
While the Premier League has not commented on the breakaway threat, the European Leagues organisation, an umbrella group which includes England's top flight clubs, said it would work together with FIFA and UEFA to stop any breakaway.
"We are determined to protect the existing model and how football is organised in Europe and the way the industry works for professional football," European Leagues president Lars-Christer Olsson said in a statement last week.
"All Football Associations and Professional Leagues in Europe are recognising and following FIFA and Confederation statutes, and this will guide us in our actions to stop this initiative.
"If the initiative is put in motion, we will coordinate our measures with UEFA, FIFA and the Confederations," he said.