Zinedine Zidane admits "the knives come out" whenever Real Madrid lose but said criticism of Marcelo after the club's midweek Copa del Rey defeat was "upsetting".
Madrid suffered a miserable 4-3 reverse to Real Sociedad on Thursday to tumble out of the cup at the quarter-final stage, and the scoreline arguably flattered the Santiago Bernabeu hosts.
Trailing 4-1 at one stage, it took late goals from Rodrygo Goes and Nacho to garner any sense of respectability.
Zidane used the match to give several of his fringe players a chance, and although 31-year-old Marcelo last month made a 500th appearance for Madrid, he is no longer the first choice left-back.
Ferland Mendy is Zidane's preferred pick now, and Marcelo, despite netting Madrid's first goal, was one of a cluster of players whose performance came in for criticism after the Sociedad loss.
The likes of James Rodriguez, right-back Nacho, goalkeeper Alphonse Areola and forward Brahim Diaz all struggled to impose themselves on the game.
But when asked about Marcelo facing flak, Zidane said on Saturday: "It's upsetting because he gives his all when he plays – not just Marcelo, all the players do – but this isn't going to change. I can say it's upsetting, it's not good because they go out there and play to their maximum.
"The fans who were there saw that. The fans have a role to play – they could be upset when we get knocked out, but I know they know we've given 100 per cent.
"I think Marcelo gave his all the other day. The knives come out when you lose. When we lose, everything gets analysed. The important thing is my players give 100 per cent and he did, I think.
"He's been an important player for many years and I'm sure he's going to continue to be important until the end of the season
"It's very difficult with 50-60 games to play your best football always, so there are ups and downs. There's a long way to go and everyone is needed until the end of the season."
Madrid are back in action at Osasuna on Sunday and entered the weekend with a three-point lead over Barcelona at the top of LaLiga.
Marcelo's fellow Brazilian Casemiro was another to sit out the Sociedad game and the midfielder's absence was felt, but head coach Zidane said the team should have been able to cope without his presence.
"We have one player in that mould. But we have other players who can come in and do a good job," said the Frenchman.
"People analyse too much the issue of if Casemiro plays or not. We all know what he brings to the side when he plays in that central position, but we need to play well when he's not available."