Defeat for Barca at the Bernabeu would leave them seven points behind Los Blancos with just nine games remaining – a gap that Martino believes would be unbridgeable.
"Yes, it is [our last chance]," he told reporters at a press conference. "There will be nine games left and having to cut back one point wouldn't be the same thing as cutting back seven.
"The big teams don't slip up so much. A draw isn't a good result – we need to win.
"We need to play well, keeping possession of the ball, building up the play well and not losing balls that allow Madrid to counter-attack."
Madrid are currently on a 31-match unbeaten run in all competitions.