The world and European champions host Valencia in a semi-final second leg match with Carles Puyol's header from the 1-1 draw at Mestalla last week giving them a slight edge in the tie.
Barca's anxious 2-1 home win over Real Sociedad in La Liga at the weekend ended a run of three consecutive draws, their worst run of results this season, and a rare barren spell for top scorer Messi.
It was only after a black cat streaked across their pitch on Saturday that Messi finally broke his run of bad luck in front of goal, which included having a penalty saved during the first leg of the semi-final.
The World Player of the Year has netted 37 times in all competitions so far, but his team have looked more and more reliant on his goals and playmaking as a lengthening injury list took its toll.
David Villa, Pedro, Andres Iniesta and Alexis Sanchez have all been laid low, forcing coach Pep Guardiola to fall back on their famed youth academy of late, but the zip has been missing from the side's play.
A nasty gash to the knee of midfielder Sergio Busquets on the weekend makes the Spanish international a doubt for Wednesday as well.
"We'll see if, little by little, we can start getting players back," Guardiola said on Saturday, when he rested other key players such as Xavi, Gerard Pique and Eric Abidal.
"The players we have available are making a titanic effort, and they have a chance on Wednesday to secure a place in the final for later in the season, while we turn our focus on the other two competitions [La Liga and the Champions League].
THE LIONS
Barca won the cup in 2009, and lost in last season's final to their arch rivals Real Madrid, who they trail in the league by seven points.
Valencia are a distant third in the standings and also going through a poor run of form.
Unai Emery's side, cup winners in 2008, were held 0-0 at Atletico Madrid on Sunday. Aside from cup games they have yet to win in 2012.
Third-tier giantkillers Mirandes face a big cat problem in the other semi on Tuesday when they travel to the intimidating San Mames to play Athletic Bilbao, known as The Lions.
Bilbao, sixth in La Liga, can look to powerful Spain striker Fernando Llorente, who has returned from injury scoring six times in three games. He netted both goals in their 2-1 first leg win in Miranda de Ebro last week.
Mirandes, who have an annual budget of just over 1.2 million euros compared to the 60 million euros or so at Bilbao's disposal, grabbed a lifeline with Ander Lambarri's injury-time goal.
They are only the second club from the Segunda B to have reached the last four of the competition in its current format.
