A shock betrayal, a beastly payback - 5 WWE Superstars who could cost Roman Reigns the world championship at Clash at the Castle

Roman Reigns will walk into WWE Clash at the Castle on September 3 to fight Drew McIntyre. He will be battling to keep his Undisputed WWE Universal Championship fully aware of how difficult his mission will be.

Reigns unified the WWE Championship with the Universal Championship and became the first Undisputed WWE Universal Champion in history. In doing so, he got the whole world to stand up and acknowledge him. By the time Clash at the Castle rolls around, he will have been world champion for a staggering two years.

McIntyre will only be keen to break that streak and create history on his home turf. While The Scottish Warrior will have plenty of hurdles to overcome on September 3, the same can be said for his opponent.

Here's a look at five WWE Superstars who could play a role in Roman Reigns losing the Undisputed WWE Universal Championship at WWE Clash at the Castle.

#5. On our list of WWE Superstars who could cost Roman Reigns his titles at Clash at the Castle: Theory

Beware the man with the contract

Roman Reigns should thank Brock Lesnar for making sure Theory didn't keep his word and walk out of SummerSlam as the champion. The Beast stopped the latter in his tracks and made sure he didn't cash in, but things might not be so straightforward this time around.

Theory has been real quiet about the Money in the Bank contract lately, which means a cash-in at Clash at the Castle would catch Reigns off-guard. Should he score a decisive pinfall after cashing in, The Head of the Table will no longer have the top gold in WWE.

#4. Sheamus and his gang help McIntyre beat Reigns

Sheamus could get involved in the main event

Sheamus is not the biggest fan of Drew McIntyre, but there is no doubt that he respects him as a competitor. The two men waged war to determine who would face Roman Reigns at Clash at the Castle a few weeks ago, and it was the latter who came out on top.

Sheamus is also someone who doesn't like Reigns and his Bloodline, and that could factor into the proceedings on September 3. He could arrive along with Butch and Ridge Holland to neutralize The Usos and Sami Zayn at ringside. This could give his European compatriot an opening to beat the champion.

The Celtic Warrior is the kind of guy to help the challenger win and then demand a title opportunity next week. Him helping The Scottish Warrior will purely be for selfish reasons, but it could result in Reigns no longer being champion.

#3. The Usos accidentally cost Reigns the title

Will we see the end of The Bloodline?

The Usos have had Roman Reigns' back for so long and have routinely saved his bacon. If they weren't there by his side, he wouldn't have enjoyed even half of the championship reign he does today. However, these things regress to the mean, and there will come a time when Jimmy and Jey slip up and cost their cousin big time.

The Undisputed WWE Tag Team Champions will no doubt try their best to screw Drew McIntyre over at WWE Clash at the Castle. However, a mistake could see the tide turn and McIntyre pounce on a helpless Reigns to become champion. Imagine the scenes if the twins accidentally superkick their Tribal Chief and hand him the biggest defeat of his career.

#2. Sami Zayn costs Reigns the title

Sami Zayn's relentless sucking up to The Bloodline hasn't paid dividends as of late. The Usos told him to step up or step away a couple of weeks ago. It's obvious to everyone except him that they don't value or rate his services.

However, there will come a day when Zayn sees what The Bloodline thinks of him. This could come as early as Clash at the Castle, causing him to exact revenge in the most brilliant of ways.

As The Usos are doing their thing helping Roman Reigns, The Honorary Uce could betray them and assist Drew McIntyre. The Master Strategist taking down the unstoppable champion would be some fantastic storytelling. Should he help McIntyre crush Reigns' empire, he will instantly become one of the hottest babyfaces on the roster.

#1. Brock Lesnar gets his revenge on Reigns

Brock Lesnar and Roman Reigns may have wrestled their final match together, but that doesn't mean their saga is over. SummerSlam saw The Bloodline screw him over again to make sure Reigns walked out a battered and bruised champion.

Lesnar could make a quick stop in Europe and hit the ring while The Bloodline are actively trying to interfere in the title match. He could emerge and clean the house at ringside so that Drew McIntyre has only the champion to focus on.

The Beast's actions would be sweet payback for the events of SummerSlam. The sight of The Tribal Chief walking into a Claymore and getting his shoulders counted down for three will be a moment to behold. It could come thanks to Lesnar, whose return and attack on The Bloodline could pave the way for a new champion to take over.