Sami Zayn's reign as WWE United States Champion could come to an end on this week's SmackDown. The Underdog from the Underground has proven himself to be a fighting champion. After receiving John Cena's blessings, Zayn has been hosting the US Title Open Challenge every week. His first opponent was The Cenation Leader himself, but their bout was disrupted by Brock Lesnar.The Canadian has since successfully defended his title against Rey Fenix, Carmelo Hayes, and NXT's Je'Von Evans. Fans are excited as Zayn is set to defend his championship once again tonight. However, it might backfire, as the former OG Bloodline member could end up losing the US Title.The former champion, Solo Sikoa, may not be done with Sami Zayn after all. However, Solo might not be the one to face Sami. Instead, he could encourage Tonga Loa to step up and challenge for the coveted championship. In a shocking turn of events, the 42-year-old could defeat Zayn to become the new United States Champion.After losing the US Title to Sami Zayn on the go-home episode of SmackDown before Clash in Paris, Solo Sikoa has been regrouping with his faction members for the last few weeks in cryptic vignettes. Two weeks ago, The Street Champion acknowledged Tonga Loa's loyalty to him and assured that it would be rewarded.As a result, Sikoa may back Loa to answer Zayn's open challenge this week. Not only that, The Street Champion could also assist the 42-year-old in defeating The Underdog from the Underground. This could be done to send a message to the rest of the roster that MFT is more united and dangerous than ever.That said, this is just speculation for now. Fans will have to tune in to SmackDown to see who steps up to Sami Zayn.Former WWE writer criticizes Sami Zayn's booking on SmackDownLast week, NXT's Je'Von Evans answered Sami Zayn's open challenge. The Young OG put on an impressive performance, coming very close to dethroning the Canadian. However, Zayn prevailed after hitting a Helluva Kick followed by a Blue Thunder Bomb to retain his title.While many enjoyed the back-and-forth bout, former WWE writer Vince Russo wasn't one of them. Speaking on a recent episode of Sportskeeda's BroDown with host Mac Davis, Russo slammed the creative team for its booking of the match.The veteran took issue with Zayn going 50-50 against an NXT star like Evans. Here's what he had to say:"What were you and I talking about just two weeks ago? Sami Zayn went 50-50 with John Cena and we were supposed to believe John Cena was supposed to bring down Brock Lesnar. Now, this jabroni from NXT comes over who I've never heard of and he goes 50-50 with the guy that went 50-50 with John Cena. What does that tell you, bro? It tells you that everybody goes 50-50 and that's why nobody's over. That's what it tells you."It will be interesting to see what the Triple H-led creative team has in store for tonight's SmackDown.