Thibaut Courtois vowed to continue fighting but acknowledged Real Madrid's LaLiga title hopes may be over after a dramatic defeat at Barcelona on Sunday.
Franck Kessie scored a last-gasp Clasico winner in a 2-1 win over fierce rivals Madrid at Camp Nou to send Xavi's side 12 points clear at the top heading into the international break.
Carlo Ancelotti's side had taken the lead through Ronald Araujo's ninth-minute own goal, only for Sergi Roberto to deservedly equalise on the stroke of half-time.
Courtois impressed with a fine individual display to keep Los Blancos in the game, though the goalkeeper conceded Madrid's defence of their Spanish crown will likely come to an end.
The Belgium international told LaLiga TV: "We have to be honest. We will continue fighting, but there are four games difference.
"We have the advantage on goals [on head-to-head record], but it is difficult. Nothing is impossible, but... we will have to come here to win in the Copa del Rey [semi-final]."
Kessie's late strike, timed at 91 minutes and two seconds, was the latest LaLiga winning goal Barca have scored in the Clasico since Lionel Messi's finish (91:48) in a 3-2 win in April 2017.
But Courtois believes Xavi's hosts would not have found a way back if Madrid could have withstood the pressure before the interval.
He added: "We played a great game. We both had chances. You go ahead, control and they strike before half-time. That affects us. With 0-1 at half-time, I don't think they would have won.
"In the second half we played well. We didn't have many chances but when they arrived we didn't take advantage of them. We were going for the victory, we left spaces and they scored a goal against us.
"I'm happy to help the team, but we haven't achieved victory. We mustn't give up. I'm sure we can come to win in the Copa del Rey and do well in the Champions League."
While Courtois suggested the LaLiga title was destined for Barcelona, Sergi Roberto refuted that message as he referenced the resilience of Madrid.
"You can never say it. There are many games left and you can never say Madrid are dead," he said. "12 points is a difficult distance to let go, but it depends on us, which is good."
Madrid thought they had snatched a late victory before Kessie's winner, with substitute Marco Asensio seeing an 81st-minute strike ruled out for offside after a lengthy VAR review.
That late drama made the victory even sweeter, according to Roberto, who added: "We came back from a goal by Asensio that we hadn't realised was offside.
"Then we scored and it tastes better winning like that, at the last minute."
Questions may have been raised by some after Sergi Roberto was preferred to start over Kessie in midfield, though the Spain international felt he repaid the backing of Xavi with his performance.
"Today it was either Franck or me and in the end we both scored," he continued.
"I am very happy to continue in the club of my life. I have only played in this club. I thank Xavi, the board, the president. It is my way of returning my love. Now we can rest during the break."