Reigning world and European champions Spain, Italy and England have made surprise group-stage exits in Brazil and Portugal look almost certain to join them.
Sabella, whose side have booked their last-16 place ahead of a clash with Nigeria on Wednesday, said it would be a tough World Cup to win.
He pointed to inconsistencies already seen in performances by his team, Germany and Italy.
"It is very equal. You have a Germany that thrashed (Portugal 4-0), but then draws (2-2 with Ghana). Italy that wins to England, but then loses (1-0 to Costa Rica)," Sabella said.
"It is a very difficult World Cup, it is played in a country that is nearly a sub-continent, with great distances, with great climatic changes, so I believe that the physical and tactical part will be very important.
"It is very important to have a squad with good substitutes so you can keep up the competition rhythm."
Sabella said he was delighted to be able to give his players a day off and allow them to enjoy their time away from the game.
"I am happy because the players could spend a day with their family, putting aside for a while the pressure and the responsibility," he said.
"I think it was a very pretty day, they enjoyed it a lot, and it was an emotion for me, seeing all of them with their families. It was a very pleasant afternoon."
