But Cardinals coach Bruce Arians and his players aren't about to change their plans.
"Anytime you're apprehensive and let ISIS or whoever it is change the way you think or what you do, they're winning," Arians said after Tuesday's practice. "We'll go and do everything we can to put on a great show. If something happens, it happens. But they're not gonna scare us off."
Cardinals linebacker Chandler Jones traveled to London with his former team, the Patriots, to play a game in the London's Wembley Stadium when he was a rookie. Like Arians, he's not worrying about things out of his control.
"I feel like that's just something we'll have to worry about when it comes," he said. "It's a touchy topic right now ... We'll figure it out, and I'm pretty sure we'll be safe and everything will be back to tracking back to normal."
Rookie wide receiver Chad Williams is confident the NFL will ensure the Cardinals' safety during their time in the UK.
"We don't have any concerns about playing over there," he said. "We know we're dealing with some of the best people in the nation when it comes to security around the NFL, and I know they'll do everything in their power and everything they have to do to keep us safe from everything."
Cards center A.Q. Shipley echoed Williams' sentiments.
"At the end of the day, our job is to go play over there," he said. "We expect them to have good security like always, and (playing football is) what we do."