Having missed the entire Six Nations campaign, Richie Rees will make his first start since his 12-week ban started at the beginning of January.
Rees was suspended after being found guilty of foul play, having made contact with the eye area of England international Dylan Hartley during the Northampton Saints Heineken Cup match in December.
The scrum-half's return is a timely boost for the Blues, as both they and the Ospreys have labelled their Magners League clash at the Liberty Stadium as a “must win” game.
The Ospreys are fourth in the table, while the Blues are five points behind them in fifth place but having played a game less.
Defeat would all but end the Blues’s hopes of reaching the Magners League play-offs, while the Ospreys can ill afford to allow the gap between them and their rivals to shorten further.
And with both sides entering the fixture on the back of defeats - last weekend the Blues lost 16-15 to Munster while the Ospreys were beaten 23-16 by Edinburgh - it could be a tense atmosphere at the Liberty.
Blues coach Dai Young said: “We have to win every game. We don’t have a good record at the Liberty, but this is the sort of game we must win.”
The Blues have not won at the Liberty since their 28-9 triumph in 2005, and the Ospreys are determined to build on their impressive home record.
Ospreys head coach Sean Holley said: “Bragging rights is always a big one but I think more importantly now it’s seen as a must-win game for both teams.”
Those bragging rights belong to the Blues so far this season, following their 27-25 Magners League victory over the Ospreys at the Cardiff City Stadium on New Year’s Eve.
The Ospreys did win the LV Cup tie at the same venue in January, though that match was fought between two reserve teams.
There will be no second-string sides in sight tomorrow, however, as the two Welsh giants collide in their final quests for a trophy this season.
Young said the Blues know the magnitude of the challenge which lies ahead. “We’ve got three Welsh derbies and they’re always difficult to win no matter where they are, “ he said.
“Every game is a cup final. We’ve got to go to these places and win. It’s a big mountain for us to climb. We’re capable of it and that’s what I’ve said to the players. But we’re going to have to be better than we were - it’s as simple as that.”