The 26-year-old Cardiff Blues and Wales star admits he and his Lions team-mates have no idea who head coach Warren Gatland will pick in the vast majority of positions but that back row is arguably the most competitive.
"One position there's a lot of strength in is centre, but it's even more so in the back row," said Roberts.
"You can pick three of any of those players and you'd have a world-class back row.
"It's a bit scary, and we can be very optimistic about that. There's probably three or four combinations that you could pick there and they'd cause the Australians bother, so that's very pleasing.
"We haven't got a clue (who'll be in the Test team). The coaches have made that clear to the players, that they'll give everyone a shot.
"This Saturday's selection will probably sway things a little, that's what people are expecting anyway. But as a side we'll wait and see."
Gatland will name his side to face the Waratahs in Sydney tomorrow at 12.45pm local time and 3.45am BST, with just one more game then before the opening international on June 22.
Roberts isn't sure whether Saturday's side will bear a close resemblance to the team that runs out in Brisbane but one thing he is certain of is that the Tahs will present tough opposition at the Allianz Stadium.
"I think Saturday will be far tougher than Tuesday was," added Roberts, who insists that The Lions won't be under prepared for the Test series despite the games against the Barbarians, Force and Combined Country bringing comfortable victories.
"The boys who played against the Reds, that was a really tough hit out against a quality team. I'm sure that Saturday is going to be as equal a challenge, if not a greater challenge than the Reds game.
"I don't think there's any danger of this squad being undercooked for the Tests. If Gats doesn't feel we're reaching that test-match intensity in games, he'll make sure we do it in training.
"It's the nature of the tour, but it's up to us as a side to raise the intensity in our game. That's maybe something we didn't do (against Combined Country). That's the frustrating thing, more than anything. We played some good rugby but it's just taking ourselves to the next level having not gone for the jugular."
The Lions scored 10 tries in Newcastle against the Combined Country but matchday captain O'Driscoll admits they didn't quite kick on in the manner they would have hoped after a free-flowing first half and Roberts agrees.
"We played a team where it's a once-in-a-lifetime game for these guys and they've provided a stern opposition," continued Roberts.
"They defended at well at times, certainly in that second half. They just spread the field and made things difficult for us. It was very greasy, there were quite a lot of knock ons and we lost the ball in contact a few times.
"The conditions are no excuse - we've got to work a bit harder at not letting go of the ball, because over the next three or four weeks it could be greasy. None of the stadiums here have roofs on them and we're in the middle of winter. That's something we've got to look at.
"I thought we played some good stuff in the first half. We attacked well, we scored some nice tries, had some good setpiece, set plays, but towards midway through the second half we didn't quite go for the jugular and that's something we'll look at."