"He could have played (last week) against Levante but he needed a few more days recuperation and now he is definitely ready to return," Mourinho told a news conference.
The Argentina winger, who has made 13 assists in the league this season, has been struggling with a thigh problem and has not played since the turn of the year.
With champions Barcelona not hosting third-placed Valencia until Sunday, a win for Real at the Bernabeu would put them 13 points clear of their arch rivals in second, although Mourinho warned against complacency.
"The situation is a good one for us and a difficult one for them, that seems obvious and logical to me,' he said.
"But there are a lot of tough games left and Barca are perfectly capable of winning 10 games in a row and if you lose one then you start to have problems," the Portuguese added.
Barca are without the suspended Javier Mascherano and Daniel Alves for the game against Valencia at the Nou Camp, meaning coach Pep Guardiola will be forced to shuffle his defensive pack.
Captain Carles Puyol, Adriano Correia or B team player Martin Montoya could replace Alves at right-back, while Puyol's place in central defence could be taken by left-back Eric Abidal or midfielder Sergio Busquets.
Barca have midfielder Seydou Keita back from the Africa Cup of Nations, where his Mali side finished third and he was selected for the team of the tournament.
Keita was given a round of applause by his team-mates at training on Thursday, as was Netherlands midfielder Ibrahim Afellay, who did some work on the pitch for the first time since he injured a knee five months ago and needed surgery.
Barca goalkeeper Victor Valdes has urged Guardiola to agree a contract extension beyond the end of this season, saying the former midfielder is a vital ingredient of the club's spectacular recent success.
"It's his decision of course but I hope he continues and for as many years as possible as he is key to this team," Valdes said.
Guardiola prefers to renew his deal with the Spanish and European champions on an annual basis and as the season has slipped by mutterings about the possibility of him leaving have grown in volume.
Sporting Gijon's new coach Javier Clemente makes his debut at home to Atletico Madrid on Sunday as the former Spain boss begins the daunting task of saving the struggling Asturians from relegation.
Atletico are on a high after a 3-1 Europa League win at Lazio on Thursday but coach Diego Simeone said they must forget the euphoria and focus on a match against a "super-motivated" Gijon he predicted would be "very tough".
"They have a very capable and very intelligent coach, who has a great deal of mental strength," former Argentina captain Simeone, who took over at Atletico at the end of last year, told a news conference after the Lazio win.
Fourth-placed Levante, who have 32 points, host Rayo Vallecano on Sunday, while Espanyol, in fifth also on 32 points but behind on goal difference, play at Getafe on Saturday.
Malaga and Athletic Bilbao, who have 30 and 31 points in seventh and ninth respectively, meet at the San Mames on Sunday and eighth-placed Osasuna, also on 31, play at Sevilla on Saturday.
In a congested lower half of the table, only seven points separate Levante in fourth from 17th-placed Granada, with Santander, Sporting and Real Zaragoza occupying the three relegation places.
Follow these matches live this weekend: Saturday - Real Madrid v Santander (19:00) and Sevilla v Osasuna (21:00); Sunday - Barcelona v Valencia (20:30)
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