"It was nearly the same faces all the time and it was a bit hard for us.
"Maybe that was the reason we did not do so well in the final stages of the Champions League.
"This season we have a bigger squad and we are in good shape going into this game."
Vidic, who returned to the side in the 1-1 draw at Blackburn after a knee injury, expects a hard shift against Barcelona.
However he has refuted suggestions he could have a key role to play in keeping Lionel Messi quiet.
Vidic said: "Of course he is one of the best players in the world, everyone knows that.
"But the game is not all about Messi. Like many good teams, Barcelona have many good players.
"We have a tough job tomorrow but we will do our best to try and contain them and get a good result."