Nani believes Manchester United are still well-placed to retain the Premier League title but cautioned the club could ill-afford another slip-up like Saturday's loss to Blackburn Rovers.
United will be hoping they can put the 3-2 defeat to Rovers behind them when they travel to Newcastle on Wednesday night, after Manchester City opened up a three point lead at the top of the table.
Manchester United's shock defeat by Rovers on New Year's Eve meant Sir Alex Ferguson's side missed out on the chance to vault their fierce rivals and current league leaders - and finish 2011 on top of the Premier League.
"If we want to fight for the Premier League title it's impossible to repeat a defeat like the one against Blackburn," Manchester United winger Nani told the Daily Star.
"Things like that could decide the title at the end of the season. It was a negative day [for Manchester United].
"But I think it represents a lesson for us and now we must not fail. It left a bitter taste in the dressing room.
"But now we have to bounce back against Newcastle. It won't be easy but we are the champions and this squad is always out to win."