Roberto Mancini is ready to drop a number of his underperforming frontline players for Manchester City's FA Cup tie against Leeds United on Sunday, conscious that his position as manager will be severely weakened if his team go out of the competition.

Saturday's 3-1 defeat at Southampton left City 12 points behind Manchester United, following Sir Alex Ferguson's team's win over Everton the following day. With only 12 matches left City's hopes of retaining the title appear remote and Mancini knows that if the side's form were to falter further then the club's hierarchy may consider his position.

When City fell eight points behind United in April last season, after appearing to be favourites to win the Premier League earlier in the campaign, Mancini was told he must at least ensure the side put up a robust challenge in the closing six matches. Even if City had not won the championship, Khaldoon al-Mubarak, the chairman, wanted evidence that the players could be rallied by Mancini and play for him. In the event City became champions for the first time in 44 years and the manager signed a new five-year deal in the summer.

Although there is no will to remove Mancini, City's dire Champions League challenge, in which they failed to emerge from their group for a second consecutive year, meant greater emphasis was placed on success in the Premier League.

The Italian will be required to ensure his players do not let the gap to United become greater and that they make a serious challenge for the Cup.

Talking about his preparations for the visit of Leeds in the fourth round, Mancini told the Manchester Evening News: "I am sure we will change that, because I will change players. I only want players who are ready for the fight in the last 12 games. I am very angry with a lot of my players and very disappointed at the performance, because it is impossible to play the way we did."

"We didn't fight for every ball. We can't always win by playing well – that is normal. Sometimes we play well and win, but you also need to be able to win because you fight for every ball, and fight against an opponent who also wants to win the game. Every team that plays against us treats it like a Champions League final, but we should know this, it is normal. We now have 12 games left, [we] need to do well in the Premier League, and we have the FA Cup – there are games left and we can do better. We need to finish the season the way we did last year."

Carlos Tevez, who was not in the match-day squad at Southampton due to personal reasons, is expected to be available again this week and Vincent Kompany is also in line to return following a calf problem.

Mancini will also have Matija Nastasic and Kolo Touré to strengthen his central defence resources following international duty.