"We have around 3 million, what we call avid fans in the U.K., who are watching week in, week out. Then we have around 8 million casual fans. Both of those numbers are growing, and on Sky Sports – which is kind of the home of the NFL in the U.K.— we are now the fifth most watched sport," Waller told CNBC on Monday.
"We feel very confident that the fan passion and the fan demand is there for us," he added.
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The NFL, which is the U.S.'s leading professional American football league, has already announced plans to stage three regular season games at Wembley in 2015, including its first-ever division game in the U.K. The schedule will include games played on consecutive Sundays in London for the first time.
The move comes as part of NFL's push to popularize American football around the world. At present, soccer is the most popular sport outside the U.S., with around 265 million people across the globe actively involved in the sport, according to FIFA, soccer's governing body.
On Monday, Waller met with U.K. finance minister, George Osborne. Osborne has said previously said that the U.K. government backs plans for an American football team to be in London long-term.