Both contests are delicately poised, with Barca somehow 1-0 down to Chelsea despite dominating at Stamford Bridge, and Madrid grabbing a potentially crucial away goal in a 2-1 loss to Bayern.
Though Chelsea and Bayern were able to rest almost their entire first-choice line-ups over the weekend in view of the second legs, their European opponents were engaged in a high-intensity La Liga grudge match in the driving rain at Camp Nou.
Madrid won 2-1 to virtually guarantee a first title in four years and will take confidence into the second leg at the Santiago Bernabeu.
Barca, however, will have to pick themselves up after a second loss in a four-day span, with their season threatening to unravel.
"I don't think we are spent physically," said Barcelona coach Pep Guardiola. "Now we have to play our best game possible. These players have been in many situations like this one and they have always risen to the occasion."
Chelsea are unbeaten in their past six matches against Barcelona and are comfortable playing in a backs-to-the-wall style, with their obdurate defence backing up their clean sheet from the first leg with another in a gritty display in the 0-0 draw at Arsenal in the Premier League on Saturday.
"It was great practice coming up against the likes of Robin van Persie, who's in form this season, and is one of the best forwards in the world at the minute," said Chelsea defender Gary Cahill.
"It doesn't get any harder, does it, this week? Facing the likes of Messi and then Van Persie and then back to Messi and the [Barcelona] boys."
Chelsea have the added motivation of perhaps needing to win the Champions League to qualify for next season's competition. They are sixth in the Premier League, four points behind fourth-placed Newcastle with four games left.
With Messi, a scorer of 63 goals this season, unlikely to go a third game without finding the net, Chelsea might need an away goal to advance to their second Champions League final and prevent their Spanish opponent from making the showpiece for the third time in four years.
Didier Drogba, who scored the winner at Stamford Bridge with Chelsea's only shot on target, is battling to recover from a knee injury.
Midfielder Cesc Fabregas and defender Gerard Pique were the only big-name Barca players not to start the gruelling match against Madrid.
Bayern are aiming to qualify for the final to be played at their Allianz Arena home on May 19 and hold a narrow lead.
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