He admits Premier League survival is more important than beating Everton next weekend and making it to a Wembley semi-final.
Martinez said: "Success in the Cup is something we want but never at the price that it would affect our league campaign.
"It's a difficult game at Everton but one game away from Wembley is a great opportunity.
"In the position we're in, after this we need to find the best possible team to carry on playing in the league. That game will give us the chance to make changes. Not to rest people but maybe to find people who deserve to be in the team and develop real competition.
"Cup runs with 11 players affect performances because it's impossible to maintain the level of players.
"But if you have a big enough squad, you can share demands and success in the Cup which can help in the league.
"That is what we have had this season. The FA Cup has helped towards the league."