Greg is part of the USA team that lost their first match in the RWC 2015 to Samoa last weekend, but he is confident they can bounce back when they take on Scotland at Elland Road, Leeds, on Sunday.
“It will be a bit weird as they will be team-mates,” said Greg in the Evening Times.
The big lock forward spent a week training with Glasgow before joining up with the American squad just before the World Cup.
“I didn't meet any of the Scottish representatives when I was up there” - Glasgow's international contingent were away with Scotland - “but I heard a lot about them.
"Maybe there will be a few awkward hugs and handshakes after the game.”
Greg, who left Leicester Tigers and signed a two-year deal with the PRO12 champions, decided it was important to meet head coach Gregor Townsend and the players before leaving for the World Cup.
“I had been in touch with the coach and I wanted to get in and meet the team,” he said.
“Joining a new team part of the way into a season is tough, so I wanted to meet as many of the players as I could to establish the bond straightaway.
“Gregor pretty much sat me down and told me the Warriors are a hard-working team and said he thought I fitted the bill for the team.
"I haven't had many opportunities in the past couple of years so I thank him for giving me a chance and I hope it pays off in spades. After the World Cup I’ll pretty much be going straight to Glasgow.”