Wales line up for their first Test against South Africa on Saturday with ten of last summer's Lions touring party to Australia in the starting line-up for the match in Durban.
Roberts, Alex Cuthbert, Jonathan Davies, George North and Mike Phillips line up in the backs, while props Adam Jones and Gethin Jenkins are joined by Alun Wyn Jones, Dan Lydiate and Taulupe Faletau in the pack.
But Roberts says the rise of Davies, as well as Rhodri Williams, could have Phillips worried.
"(Davies) was the form scrum-half in Welsh, if not British, rugby this season," Roberts told Wales Online.
"He has some serious pace and he is a very dangerous player. He likes taking the ball on the fringes and he will pick off defences. He is in an environment full of experienced international players and it is only going to improve him.
"With Rhodri Williams there as well, the competition has spurred Mike Phillips on at scrum-half.
"I have played club rugby with Mike this year and he knows the other nines in this squad are very good players who have had very good seasons.
"It has been great for Mike as he has had to raise his game and he knows what is expected of him this weekend. He is a world class player, he has thrived here before and I am sure he will do the same."