Real Madrid full-back Marcelo hailed Casemiro as one of the best midfielders in the world following his match-winning display against Athletic Bilbao.
The Brazilian struck a second-half winner to seal maximum points after Aritz Aduriz had cancelled out Karim Benzema's opening goal at San Mames.
The goal capped a hugely impressive all-round performance from the 25-year-old and his compatriot believes he has come on leaps and bounds in recent seasons.
"Casemiro has improved amazingly," he told BeIN Sports. "He works very hard and it's a privilege to play in the same side as him. He's got to be one of the best central midfielders in the world."
Marcelo criticised the team for failing to carry out Zidane's instructions in the wake of their 3-3 draw with Las Palmas, but he commended his team-mates for their efforts in a tough encounter on Saturday.
"Every game here is really difficult," he said. "They move the ball really well, but the boss told us we'd have to give everything on the pitch and that's what we did.
"We worked this week, we had a lot of time to prepare for the game and it went well for us. We did everything the boss said out on the pitch.
"It's important to win, of course. Our objective is to keep getting points when we can. It was important to get to the international break at the top of the table."
Aduriz, who equalised for Athletic just three minutes before Casemiro's winner, felt his side were punished for not adding a ruthless touch to a good performance.
"I don't really care about the goal. It doesn't matter if you score if it doesn't help the team to win," said the striker.
"I think we dominated the play and we got close to Madrid's area, but maybe not with the precision we wanted. We worked really hard.
"They had chances, but Madrid always have chances. You have to be really efficient if you want to beat them. They have players up front with so much quality."