In the fictional universe of "One Punch Man," Saitama is an incredibly powerful character. He possesses unmatched strength, speed, and durability, capable of defeating virtually any opponent with a single punch. However, there is no definitive evidence or depiction in the series that suggests Saitama can destroy an entire universe.
The extent of Saitama's power is not fully explored or defined in the story. While he effortlessly defeats opponents who are considered planet-level threats, it is unclear how his power scales beyond that. The series primarily focuses on his ability to defeat enemies with ease rather than exploring the scope of his abilities.
It's important to note that the destruction of a universe typically requires an immense amount of power on an unimaginable scale. The concept of universal destruction is often reserved for characters in more cosmic or multiverse-oriented settings, such as characters from Marvel or DC Comics.
In summary, based on the available information from the "One Punch Man" series, there is no concrete evidence to suggest that Saitama can destroy an entire universe. His power remains undefined beyond the context of defeating opponents within his own fictional world.