"We don't lose anything by losing Rhys," Roberts told talkSPORT. "James has shown over the last four of five years what a central role he has played for Wales, especially in the number ten shirt."
Despite the glimmer of a semi-final in sight, the 24-year-old centre believes the team aren't getting ahead of themselves.
"It's an amazing occasion, I don't think any of the players would dispute it's the biggest game of their careers," he added. "But at the end of the day it's a game of rugby."
The showdown between Wales and France takes place on Saturday at Eden Park.