Marcelo has accused Real Madrid of failing to implement their game plans following their 3-3 draw with Las Palmas on Wednesday.
Isco put Madrid ahead at the Santiago Bernabeu but Tana netted a quick-fire equaliser, and goals from Jonathan Viera and Kevin-Prince Boateng turned the match on its head after Gareth Bale had been sent off.
Cristiano Ronaldo scored twice in three minutes in the closing stages to rescue a point for Zinedine Zidane's side, but the result was not enough to see them retake top spot from Barcelona, who had earlier thrashed Sporting Gijon 6-1.
Madrid still have a game in hand that could send them back to the summit but Marcelo has admitted that they must make huge improvements if they are to end a five-year wait for the title.
"It was difficult once more. We have to improve lots of things and we'll continue to look forward," he told Movistar+.
"Before the games, we speak about things that we then don't do and then this is what happens.
"Las Palmas have great players. In the end we drew the game, I don't know how. It's very difficult."
Bale was dismissed two minutes into the second half, the Wales star picking up a booking for a petulant kick at Viera before being shown another yellow card for shoving the midfielder to the floor.
It was Bale's first red card since joining the European champions in 2013 and Marcelo claimed it was not his place to criticise the forward in public.
"I'm not the one who has to give a telling-off," the Brazil full-back said. "Bale is old enough to know what he has to do and whether or not he's wrong."
