City host the Championship side in the last eight on Sunday before travelling to Spain when on Wednesday they must overturn a 2-0 first-leg defeat by Barca to reach the quarter-finals.
"We are just thinking about the game against Wigan. We know it is a tough game, and it will not be an easy game. They are playing very well, and have won their last four games. When we finish the game on Sunday we will start thinking about Barcelona," Pellegrini told a news conference on Friday.
Wigan claimed one of the greatest FA Cup final upsets of all time when a 90th-minute header from substitute Ben Watson stunned hot favourites City in last season's showpiece game at Wembley.
City exacted revenge with a 5-0 demolition of Wigan in the League Cup third round in September and went on to win the trophy on Sunday with a final victory over Sunderland.
Wigan, who became the first club to win the FA Cup and be relegated from the Premier League in the same season, sacked manager Owen Coyle in December with German Uwe Rosler, a former City striker, taking charge.
Rosler has guided Wigan into the playoff places and Pellegrini expects a tougher test than they were given by the Latics earlier in the season.
"I think it is a different team today and it is difficult," the Chilean said.
"I know Rosler has an important link with this club but now he is the manager of Wigan and he will want to win."
"It was very useful for Sergio to play the 55 minutes with his national team (in midweek) and he also played the same amount of minutes in the final, so every game he will improve," he said.
Pellegrini said the only pressure on his side was "to win on Sunday" and not worry about their challenge for honours in other competitions.
"It is very good for the squad at this stage of the season to have a chance to win all competitions, but it is not a target we are under pressure to achieve."
"It is very important for me to always work under pressure, but we are not thinking that we are going to win all the domestic titles or international titles, we are just trying to win every match.
"The only pressure we have is to win on Sunday."
- Sports & Recreation
- Uwe Rosler