However, neither of those absentees looked like affecting Barca as they were quickly in control against an Copenhagen side who, as well as winning both of their opening Group D matches, are enjoying a record-breaking start to their domestic campaign and boast a massive 12-point lead at the summit after only 12 rounds.
Barca came within inches of taking a fourth-minute lead when David Villa`s measured shot came back off the crossbar, and soon after that Maxwell saw a shot saved by the legs of visiting goalkeeper Johan Wiland.
Wiland then saved a header from Messi as Barca continued to push forward.
Messi was not to be denied two minutes after that, though, as he left Wiland with no chance to save as Barca took a deserved lead.
Spanish World Cup winners Gerard Pique and Andres Iniesta combined before feeding the ball into Messi 25 yards out from goal, and the reigning FIFA World Player of the Year took one touch before unleashing an unstoppable shot into the top corner of the net.
Villa drew another save from Wiland with a well-struck effort in the 32nd minute as Barca, who beat Panathinaikos 5-1 in their previous home match in the Champions League before drawing 1-1 away to Rubin Kazan, looked to increase their advantage before the break.
However, Pep Guardiola`s side struggled to get that second goal to settle them down, and FC Copenhagen started to make life increasingly uncomfortable for them in the second half.
The closest Stale Solbakken’s men would come was in the 66th minute when Dame Ndoye`s brilliant dipping effort from the edge of the box came back off the bar with Valdes` replacement Jose Pinto beaten.
The rebound then looked set to be headed in by Cesar Santin but the striker, who scored a hat-trick in Saturday`s 5-0 league mauling of Odense BK, contrived to nod wide with an open goal at his mercy.
That was a huge let-off for Barca, but there were still some more nervy moments to come for the Catalan giants.
After Villa had been thwarted at point-blank range by Wiland, Barca needed a last-ditch tackle from Dani Alves to deny Cristian Bolanos before FC Copenhagen captain William Kvist almost scored with an audacious lob from inside the centre-circle, Pinto racing back to palm it away.
That was in the 87th minute and Barca fans must have been bracing themselves for a tense final few minutes.
However, it was the 2009 European champions who finished the stronger, Alves seeing a low shot come back off the far post before Messi sealed the win when Eric Abidal`s mis-hit cross landed kindly for him six yards out and he rolled in his 29th Champions League goal.