The Blue and Blacks sealed cup glory for the first time in 22 years last season with hooker and captain Tomlinson a stand-out figure and Roberts in fine form at scrum-half.
Both players have now left the club. Ex-Ospreys scrum-half Tom Habberfield and former Cardiff Met and Ealing Trailfinders man Ben Williams to fill the No 9 void.
“We weren’t able to agree new terms with Martin when he came out of contract at the end of the season and at the moment he is without a club,” explained Cardiff head coach Steve Law.
“We’ve brought in Tom and Ben to fill the vacancy at scrum-half and unfortunately Joey has gone to live and work in Canada for a little while. He’ll be a huge miss.”
Cardiff finished second in the Premiership last term in what was their best campaign for a long time, but Law has also seen hard-running centre Will Rees-Hole depart.
“Will is taking a year out,” added Law. “I’ve told all the players to expect the toughest pre-season ever because the 12-team Premiership next season is going to be harder than ever. We’ve got a lot to build on and a lot to aim at.”
Last season’s RGC 1404 skipper Evan Yardley is coming in to fill the hooking gap left by Tomlinson and he will have the support of new props Ollie Drake, who is joining from Championship winners Pontypool, and Bedwas front row giant Brynley Toms.
Law has also recruited two more players from his former club, Bedwas, in outside-half Joe Scrivens and back-row man Nathan Hudd. Also boosting their back-row stock will be former Llanelli player Lloyd Pike and ex-Dragons and Wales Under-20 star James Thomas.
Behind the scrum another Wales Under-20 and Dragons player, Barney Nightingale, is tailor-made to take over the midfield role vacated by Rees-Hole, while ex-Cross Keys skipper Leon Andrews returns to his first club at the age of 35.
Andrews, equally at home across the back three and at centre, made 99 appearances for the Blue & Blacks between 2002-07 while winning Wales age grade caps.
Another top-flight recruit behind the scrum is ex-Edinburgh and Dragons centre Sam Beard. The Kiwi was released by the Dragons last year.
