The Argentina forward damaged a hamstring in Tuesday's 2-2 Champions League draw at Paris St Germain and has been ruled out of the clash at the Nou Camp when Barca will seek to protect their 13-point lead over second-placed Real Madrid.
Messi's importance to the Catalan giants extends beyond his goal-scoring exploits.
As well as netting 43 of Barca's 90 goals in La Liga and eight of 17 in the Champions League this season, he has provided a total of 13 assists in the two competitions, second only to Andres Iniesta, who has one more.
The last time Barca lost Messi to injury was in Nov. 2009 when he was out for a week and missed a Champions League Group F game at home to Inter Milan which Barca won 2-0.
It is still unclear how long he will be sidelined this time and Barca have not ruled him out of Wednesday's return leg against PSG.
Fullback Daniel Alves, who provided the exquisite pass that sent Messi clear to score on Tuesday, said the Argentine's absence was a chance for other players in the squad to step up.
"The fact that we don't have him is an incentive to prove to everyone that we have enough quality to compete without him and show that we can do it just as well as when he's here," Alves told a news conference on Wednesday.
As well as dealing with Messi's absence, coach Tito Vilanova will need to reshuffle his defence for Mallorca's visit with the injured trio of Carles Puyol, Javier Mascherano and Adriano all unavailable.
Vilanova, who returned to Spain at the end of last month after cancer treatment in New York, may opt to drop Sergio Busquets or Alex Song back from midfield to partner Gerard Pique or deploy 22-year-old youth team product Marc Bartra.
Alves has also played at centre back in the past and offered his services again if required.
"If I remember correctly, I played in that position with Guardiola when we played a back line of three," he said.
"It's easy for me to adapt. If I'm asked to attack, then I attack; if I'm asked to defend, then I defend, and if I'm asked to do both, I do my best."
With Champions League quarter-final, second legs to negotiate during the week, Barca, Real and Malaga are all playing on Saturday.
Real host mid-table Levante (1600), while Malaga can climb above Real Sociedad into fourth and boost their chances of qualifying for Europe's elite club competition again for next season if they can beat the Basque club in San Sebastian (1400).
Atletico Madrid, a point behind Real in third, play at another Madrid-based club, Getafe, on Sunday (1700).
Atletico are fully focused on securing third spot and a place in the Champions League after last term's Europa League winners were knocked out of the competition by Russian side Rubin Kazan in February.
At the other end of the table, bottom side Deportivo La Coruna can boost their survival hopes with a win at home to fellow strugglers Real Zaragoza, who are three points above the relegation places in 17th, on Saturday (1800).