Barca were held to a 1-1 draw by Sociedad on Sunday and, with Real beating Sporting Gijon 2-1 on Saturday, Los Blancos are now six points clear of their Catalan rivals at the top of the table.
The Camp Nou giants have already lost two and drawn three of their 13 games and there is a sense that the air of invincibility that used to hang over the club has vanished at present.
Whether that remains to be the case only time will tell but Eusebio believes that Luis Enrique will need to rally his troops, who were second best in many aspects of Sunday's draw.
"We were superior to Barcelona in many facets of the game," he said. "We knew it was going to be very difficult but we played a complete game. We could have won although a draw against Barca is still a good result.
"There is still a long way to go for them. They have great players, with a lot of experience and a great mentality. But they need to improve on certain aspects of the game."