Undefeated Real have a one-point advantage over champions Barcelona after nine matches and have so far faced mainly mid- to lower-table opposition, scoring 19 goals in their last four outings.
Barca, who host Real at the end of the month, play at Getafe on Sunday having defeated Sevilla (5-0) and Valencia (2-1) at home. They also won 2-1 at Atletico, who are sixth in the standings.
"We managed to avoid defeat in an important match and we want to carry on in the same vein," the World Cup winner said on Real's website.
The Uruguay striker, who has been below his best since finishing joint top scorer at the World Cup, suffered a slight sprain but was included in the squad for Thursday's Europa League match against Norwegian side Rosenborg and came through a training session in Trondheim on Wednesday.
Ranieri's successor, Quique Sanchez Flores, said it was to be expected that Forlan would have a dip in form after his exploits in South Africa.
"All the players who made a big effort at the World Cup have problems in the first few months of the domestic league season and we knew it was going to happen," he told a news conference.
"That's why we are trying to give him as much space and time as possible to recuperate."
