Samoa scrum-half Kahn Fotuali'i ranks his former Northampton team-mate Samu Manoa as one of the best players in the world.
Manoa left Northampton at the end of last season to join Toulon and the USA forward will face Fotuali'i on Sunday when they take on Samoa in Brighton.
"Samu is a fantastic all-round player and an amazing athlete," said Fotuali'i.
"He is one of the best forwards I've seen and I'd pick him in a World XV.
"He is not just a strong man, he is also very smart and never gives away silly penalties and we'll have to show him a lot of respect."
Focusing on the USA as a whole, Fotuali'i revealed that Samoa were impressed by the threat posed by the Americans' back-row and back-three players, even though the Samoan squad are high on confidence.
"We certainly won't underestimate the Americans. They have a quick back-row and some very fast backs and they will be a threat. But our team as a group has its goals and we can do very well at this World Cup," he added.
"The match against the All Blacks in July was an awesome experience for us and I think it showed we have what it takes."