New Chiefs star Rees-Zammit is seen in the Man United end at Stamford Bridge

Rugby star-turned Kansas City Chief Louis-Rees Zammit was spotted in the crowd at Stamford Bridge during Chelsea's stunning 4-3 comeback win over Manchester United on Thursday.

Rees-Zammit, who joined the two-time reigning Super Bowl champions last week, was seen on camera among the traveling United fans in the away end.

The 23-year-old is a noted fan of the Red Devils, who took a second-half lead through an Alejandro Garnacho header - before a pair of Cole Palmer goals deep into stoppage time gave Chelsea all three points.

Rees-Zammit shocked the rugby world when he quit the sport in January and embarked on the International Player Pathway to pursue a career in the NFL.

And he impressed at his IPP pro day last month as he posted a 4.43 40-yard dash, as well as a 29-inch vertical jump.

Ultimately, after reportedly meeting with several teams, he signed with the Chiefs.

According to Spotrac, Rees-Zammit's deal is worth a total $2.85million over three years.

The Chiefs confirmed the signing of 'Rees-Lightning' on social media Friday afternoon asking Chiefs Kingdom to give the Welshman a warm welcome.

'Hey Chiefs Kingdom, Louis Rees-Zammit here. Just signed, can't wait to go and see you all at Arrowhead,' Rees-Zammit said in a short video message shared to the Chiefs' social media.

The former British and Irish Lions youngster is also understood to have visited the New York Jets , Cleveland Browns and Denver Broncos after making a superb impression at the IPP with his pace and power, according to NFL Network's Ian Rapoport.

He will wear the No 9 jersey on Kansas City, and is expected to play running back.

With Thursday's defeat, Rees-Zammit's favored United are now 11 points back of fourth-place Aston Villa with just eight games to