Many people labelled the tweet insensitive, claiming it made light of a race issue that has gotten worldwide attention.
Glassman has since apologised for the offensive post, claiming he made a "mistake" and is "not racist".
CrossFit is a high-intensity interval training programme which has centres across the world, including New Zealand and Australia, which pay an annual fee to be an affiliate gym.
Its highly popular form of exercise has also spawned the CrossFit Games as well as making a slew of its devotees into bona fide CrossFit stars.
Over the weekend the fitness company's US-based CEO Glassman sparked fury when he tweeted in response to a tweet by the Institute for Health Metrics and Evaluation which said racism and discrimination were "critical public health issues".
"Floyd-19," Glassman wrote in response, referencing the killing of African-American man George Floyd, whose death in police custody has sparked the worldwide Black Lives Matter movement.
The backlash against Glassman was swift, with followers calling out his tweet as "tone deaf" and "disgusting".
The response to Glassman's tweet within the CrossFit community was swift as well, with multiple gyms and athletes immediately disowning the fitness brand.
Gyms said they would be no longer be paying their affiliate fees as they did not want to be branded as CrossFit centres in light of his comments.
James Newbury, a star athlete who has been named Australia's fittest man four times, shared an emotional video in which he said he was "out" of CrossFit until "drastic changes are made".
Glassman's tweet also didn't sit well with one of CrossFit's biggest supporters, with Reebok confirming yesterday it was ending its commercial partnership with CrossFit.
"Our partnership with CrossFit HQ comes to an end later this year. Recently, we have been in discussions regarding a new agreement, however, in light of recent events, we have made the decision to end our partnership with CrossFit HQ," Reebok said in a statement to Footwear News.
"We will fulfil our remaining contractual obligations in 2020. We owe this to the CrossFit Games competitors, fans and the community."
Glassman later responded to the criticism by seeming to try and offer further explanation to his original tweet.
"Your failed model quarantined us and now you're going to model a solution to racism? George Floyd's brutal murder sparked riots nationally," he wrote.
"Quarantine alone is 'accompanied in every age and under all political regimes by an undercurrent of suspicion, distrust, and riots.' Thanks!"
CrossFit has now published an apology from Glassman on their official Twitter account labelling his "Floyd-19" tweet a "mistake" but "not racist".
He said that he had been trying to "stick it to" the Institute for Health Metrics and Evaluation and had been "incredulous, angry, and overly emotional" when he wrote the tweet.
Glassman is still yet to delete his original "Floyd 19" tweet that sparked outrage.
