Toure is serving the last game of a three-match ban in a blow to City's chances of getting a positive result at home in the first leg of the last 16 tie.
Pique said there was a recognisable difference to Manuel Pellegrini's men when the Ivory Coast international was absent.
"Toure is a very, very important player. He was at Barca. Now he is a more attacking player," Pique told a news conference.
"When he plays and when he doesn’t, there is a difference, but we just have to look at ourselves."
Pique expects a similar tie to last season, when Barca claimed a 4-1 aggregate victory over City.
The defender said Martin Demichelis' sending off in the first leg, which Barca won 2-0 in England, saw the scoreline perhaps flatter his team.
"I think it will be a similar game to last season. We are two sides who like to attack and have the ball," Pique said.
"There was a key moment in the first leg with Demichelis' sending off and the goal from the penalty spot, without that it would have been closer."
Barca come into the first leg after a shock 1-0 loss to Malaga in La Liga, but Pique played down the significance of the defeat.
"The defeat the other day was not as painful as the loss in Anoeta [against Real Sociedad]," he said.
"When we had won 11 games in a row, nobody was talking about that. We will show that in upcoming games and we will get good results."
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