After defeating Osasuna 6-1 on aggregate in the Copa del Rey the Catalans will play bitter rivals Real Madrid in the quarter-finals of the competition, the first-leg taking place on Wednesday.If Madrid defeat Mallorca on Saturday, Barcelona could go into the game against Pepe Mel's men eight points behind the leaders, and Guardiola has conceded that only victory will do against Betis this weekend."If we do not react well in the league [against Betis] because of the Clasico, we will be out of the title race. With a rival like Madrid, you have to take all the points. Tomorrow we will go into the game 5, 6 or 8 points behind but we will have to play our game and see where we are," the 40-year-old told reporters during his press conference.The coach stressed the importance of doing well in the league and spoke philosophically about his team's hopes to retain their domestic title."I've said many times, the league is the most important for us because that is what puts you in other competitions. If my team react well we will take more points. We will play against Betis, try and win every game and at the end of the season, see what we deserved," he said.Guardiola's conference was concluded with the coach refuting claims he would add to his squad in the transfer window - instead stating he will put faith in youth."We will fall back on our youth players until the end. Going to the transfer market doesn't guarantee anything. From the very beginning we designed a small squad because we believe in our youth programme," he added.Barcelona will be looking to maintain their unbeaten home record this season, a run that has seen them score 39 times in nine games and concede no goals in Liga.