“I think the decision was made by the performance against Rico Verhoeven,” Smith said on talkSPORT. “He recognized there that he was deteriorating somewhat. He was not at the top of his game anymore.”

Smith believes Usyk has little left to prove after becoming the undisputed champion at both cruiserweight and heavyweight, defeating every major rival of his era, many of them twice.

“Why undo that legacy?” Smith said. “He’s achieved everything and more. I think he needed time himself to make that decision.”

Former British champion Spencer Oliver reached a similar conclusion, saying he noticed physical signs that Usyk was no longer able to perform at the level that made him one of boxing’s pound-for-pound greats.

“What I noticed in my last fight, my brain could see it, but I just couldn’t pull the trigger on it,” Oliver said. “I think that’s age.”

Oliver added that Usyk looked reluctant to throw punches against Verhoeven and was unable to make the in-fight adjustments that had defined so many of his biggest victories.

“He looked elderly. He looked tired,” Oliver said. “He was seeing stuff, but he was not moving. He wasn’t doing the things he normally does. I think that was the deciding factor for him recognizing that maybe he’s just one fight away from being one fight too many.”

Usyk vacated the WBC, WBA and WBO heavyweight titles earlier this week after announcing he plans to have one final fight before retiring. The move opens the door for a up-to-date generation of heavyweights to compete for the vacant championships while allowing the 39-year-old to finish his career on his own terms rather than risk diminishing the legacy he spent nearly two decades building.