Chael Sonnen recently weighed in on the hot take that a fight with Reinier de Ridder could prove to be Khamzat Chimaev’s biggest test.The Dutchman’s appeal as a challenger lies in his grappling proficiency and unorthodox style. De Ridder is regarded as a proven submission artist at middleweight.He blends high-level jiu-jitsu with suffocating grappling and clinch exchanges. His ability to control positions and threaten from top or bottom has led some to argue he could drag Chimaev into deep water on the mat.A fan on X suggested that de Ridder poses a bigger threat to Chimaev than No. 2-ranked Nassourdine Imavov. They wrote:"I feel more confident in RDR submitting Chimaev from his back than Imavov KO'ing or winning a decision. RDR has the size and the ability to drag the right into his guard, Imavov doesn't."Sonnen disagrees strongly, and replied:"Nobody wins a fight from their back. I know that sounds like a broad statement, and I suppose it is, but it’s very true. No top guy in any division has lost to a guard in close to 17 years."Check out the full exchange below:It's worth noting that de Ridder has competed at light heavyweight and carries a size advantage that few middleweights can bring against Chimaev. He also owns an unbeaten UFC record capped by a narrow win over Robert Whittaker.Kelvin Gastelum reveals Reinier de Ridder is a serious threat to UFC champ Khamzat ChimaevKelvin Gastelum has shared the octagon with some of the best competitors in the welterweight and middleweight divisions. The veteran UFC fighter believes Reinier de Ridder is the man who could give Khamzat Chimaev his toughest test.With Chimaev fresh off his title win over Dricus du Plessis, contenders like Nassourdine Imavov and Anthony Hernandez remain in the mix, but Gastelum sees de Ridder as the most serious threat to the champion’s reign.Speaking in an interview with MMA Fighting, Gastelum said:"Man, I really think RDR is someone to look at as a serious threat. I think he’s the man that could be the one. His size, his style is something to deal with, man. I mean, look, when I saw him fight against [Robert] Whitaker, I was blown away, like the size difference. I fought Whittaker, and I know how big he is. He made him look like a lightweight.”