Ever since winning the United States Championship, Sami Zayn has been working relentlessly to restore the title's prestige. The 41-year-old has vowed to be a workhorse champion as he has been issuing open challenges every week, putting his gold on the line. However, Zayn could lose the coveted title against a debuting WWE star during one of his upcoming defenses.NXT star Oba Femi could make his main roster debut on SmackDown and dethrone the Canadian star. He recently lost the NXT Championship to Ricky Saints at No Mercy after a dominant run. Since then, rumors have been swirling that Femi could be heading to the main roster. His 263-day title reign in NXT established him as a top-tier star.Hence, it may be time for The Ruler to shine under the bright lights. What better way to make his main roster debut than by accepting Sami Zayn's United States Championship open challenge? If it happens, there is a high chance that Oba Femi will dethrone Zayn on his SmackDown debut. It could end up being one of the biggest shockers in recent times.WWE holds Femi in high regard and views him as a future star. Therefore, the company might be looking to book his RAW or SmackDown debut in a major fashion that could create a lasting impact. Defeating a veteran like Sami Zayn on his very first night to win the United States Championship could create shockwaves and make The Ruler truly look like a star.However, this is entirely speculative and it remains to be seen what Triple H has in store for Oba Femi on the main roster. Also, it would be quite fascinating to see whether Zayn's title reign is heading to an end.Sami Zayn to move to the world title picture ahead of WrestleMania 42?Sami Zayn is currently on red-hot momentum as the United States Champion on SmackDown. Within a short time, the 41-year-old has established himself as a fighting champion, giving some incredible matches. However, Zayn's title reign could be a short one, as WWE may have different plans for him.There is a high possibility that the Canadian star could move to the World Title picture starting next year. Sami Zayn has been relentlessly chasing the ultimate prize for the past few years. Rumors have been swirling that he could win the Royal Rumble next year to finally set out on his chase for the World Title.This could all happen after Zayn loses the United States Championship. WWE may have given him the coveted title to build him for a big moment down the line. Besides, there wouldn't be many options left for the Canadian star after he drops the US Title. Hence, his storyline could eventually pivot to the World Title.However, this is entirely speculation and it all depends on what WWE's creative head, Triple H, has in store. Sami Zayn's future in the company will surely be exciting to see for the fans.