The 33-year-old sustained the injury in his defeat to Deron Winn in June 2019, losing on a decision in his UFC return more than a year after being released by the promotion.
Spicely had been due to face Markus Perez on Saturday before needing hospital treatment in the days leading up to the fight, suffering problems as a result of his attempt to cut weight while taking medication as a result of his trauma.
“This was my first weight cut since starting antidepressants due to the head trauma I sustained in the Deron Winn fight,” he revealed, responding to news of his late withdrawal from the event in Las Vegas.
“Needless to say, it went horribly wrong and my fight is off. I wouldn’t change a thing about my decision to do this.
“It’s maybe the worst concussion I’ve ever had. It’s not just from that fight – I’ve been punched a lot.
“I will figure it out and find a way. We all know what we sign up for.”
Brazilian Jiu-Jitsu specialist Spicely beat Thiago Santos in Brazil in 2016 but was stopped early in his last three UFC scraps before returning to CES MMA for two victories.
He received support and praise for his honesty on social media, telling fans: “I finally feel the best I’ve ever felt but the side effects are hell. I’ll be back.
“I’ve never experienced this in my life but I also feel the best I’ve ever felt mentally.”
Asked whether he thought fighting was worth the consequences he had experienced, Spicely replied: “Trust me, I thought about [retiring]. But at the end of the day, it was [worthwhile].”
UFC newcomer Charlie Ontiveros is expected to step in against Perez on the undercard of a fight card that features the headline middleweight clash between Derek Brunson and Edmen Shahbazyan.