Larger than life, not afraid to speak his mind: the former Tottenham, Rangers, Chelsea and England defender has much in common with Keane. Both won multiple trophies, captained their sides to glory, played for their countries and have been embroiled in controversy.
Roberts, 46, won two FA Cups and a Uefa Cup with Tottenham, a Scottish title and league cup with Rangers, and the old Second Division with Chelsea. Fourteen years of management, mainly in England's non-league, have also brought a haul of silverware.
Both men have recently relocated to Scotland, and both started the season with Manchester United, in a fashion. Keane swapped Old Trafford for Celtic Park, aka Paradise, last month. Roberts swapped Paradise - or rather his job as head coach at the Marbella Paradise of Football academy - to become First Division Clyde's manager eight months ago.
Clyde's headline pre-season fixture was a friendly visit by Manchester United. They lost 5-1 to Van Nistelrooy, Rooney and Co. Keane did not play, although he seems certain to appear at the Broadwood Stadium this weekend. Roberts is relishing the prospect.
"Roy will know he's been in a game," he laughs. "We're not concentrating on individuals. We know what Celtic are very good at and what they're sometimes bad at. We'll work on both."
Roberts is generous in his praise for Keane. "It's been an amazing season up here already and his move has given it another boost. I think he'll cruise through in Scotland. He's such a professional. He will want to win every game and the players around him will know that. The fella's a top professional and deserves every accolade he's ever had."
As for any suggestion that Keane is somehow taking an easy option at Celtic, Roberts laughs it off. "Apart from having a strong affiliation and a passion to play for them, Glasgow's a wonderful place to be. A fantastic lifestyle, friendly people. As for the pure football, apart from probably Manchester United, Arsenal, Chelsea and Liverpool, then Celtic and Rangers are the biggest clubs in Britain.
"Celtic are a massive football club, there are few anywhere in Europe with bigger crowds. You're almost guaranteed Champions' League football every year. And as a top-level footballer, that's where you want to play, to test yourself, and win football matches."
Keane's debut adds spice to the Cup tie. "Added spice," corrects Roberts. "It's a big game. People all over the world have been after tickets. The atmosphere will be electric. And now [Keane] has added a great element. But the spice was there anyway."
That is an understatement. Roberts' assistant manager, Joe Miller, is a former Celtic forward, and at 38, is also still playing for Clyde when required. Roberts' history with Celtic is the spiciest. And after the so-called "shame game" in October 1987, he was one of three Rangers players who ended up in court on breach of the peace charges for on-field incidents. Chris Woods and Terry Butcher were found guilty.
The case against Roberts, who had conducted the Rangers' fans' chants and singing, was not proven.
That has surely affected his relationship with Celtic? "I haven't got a relationship with Celtic," he says. "Joe and I went to the Hearts-Celtic game last Sunday and Joe made me park at the Celtic end. I had to walk along the road with all these Celtic fans giving me dog's abuse. But you just keep on walking.
"I've got nothing to hide, and I'm not going to hide from anybody. Rangers have always been my team. I'm not going to change that. And just like we looked to beat Rangers in the CIS Cup earlier this season, I'll be looking to beat Celtic in the same way."
In that CIS Cup game, Clyde came within 15 minutes of shocking Rangers, leading 2-1 until the Scottish champions scored late and then won 5-2 in extra time. "We've improved since then," Roberts says. "There's no better platform than Sunday to show it."
For a small, cash-strapped club to meet both Old Firm teams in cup competitions in one season has been a major financial blessing. Clyde's entire budget for the season is around £300,000. The Rangers game netted around £110,000 and the Celtic match will bring a profit of around £150,000.
Clyde have a proud history, winners of the Scottish Cup three times, and finishing third in the league behind the Old Firm in the 1960s. But a year ago they were almost bust. In fact, only when Roberts arrived for interview did they drop plans to go part-time. They had only two players on the books.
A mass trial attracted 2,500 hopefuls, who were whittled down to the current squad, mainly youngsters released from big clubs. Most still live with their parents. The average age of the team is below 21. Roberts raves especially about the striker Tom Brighton (ex-Rangers, 21) "who could become a superstar" and the midfielder Stephen O'Donnell (ex-Dundee United, 22) "who's got everything, I've seen nothing like him".
His message to his players before kick-off will be simple. "Work hard and you'll get your just rewards. I know that. As a player I came from the non-league. The boys are looking forward to it. It's a chance to show managers who released them what they're missing. For myself and Joe it's a chance to pit our wits against the best manager in Scotland at the moment, Gordon Strachan. He's proved that, where he is in the league."
A pause, and another smile. "And I'm sure the boy [Keane] will enjoy himself, coming to us."