The Spain international has been sidelined since injuring his left thigh muscle at last month's Club World Cup. Barca have 39 points from 15 matches, two ahead of second-placed Real Madrid, who play at Osasuna on Sunday.
Real's Brazil playmaker Kaka is recovering well from a groin problem and trained as normal on Friday, the club said on their website.
Dutch midfielder Rafael van der Vaart also returned to full training after working apart from the rest of the group for the past few days, the club added.
Villarreal coach Ernesto Valverde is not letting his players be distracted by the fact that Barca will likely be missing several key players, including Lionel Messi and Yaya Toure, for the clash at the Nou Camp.
"The great teams have good squads and you don't win titles with just 11 players," he said on the club website.
"Barca have some key absentees right now but they have top quality people to replace them."
Villarreal's recent run of three straight La Liga wins means it's a good time to play Barcelona, said their French midfielder Robert Pires.
"We are going there with a lot of respect but without fear," he told a news conference on Friday. "We know that we are going to suffer but this team has the character to hurt Barca."
Atletico Madrid forward Sergio Aguero and defender Pablo Ibanez will miss Saturday's match at home to third-placed Sevilla due to injury, the club said on their website.
"Pablo won't make it as he has been suffering from stiffness all week and (Aguero) would have only made it just in time and we are not going to force things," coach Quique Sanchez Flores said at a news conference on Friday.
Sevilla coach Manolo Jimenez still considers Atletico a direct rival despite the Madrid club's poor start to the season and their slump to 15th out of 20 in the standings.
"They are a magnificent team, one of the greats of Spanish football, but football is football and there are things that defy explanation," Jimenez said at a news conference. "I see them as a direct rival and we have to take them very seriously because they won't be down there at the end of the season."
Sevilla will be without strikers Frederic Kanoute and Luis Fabiano and midfielder Didier Zokora but goalkeeper Andres Palop should be fit, Jimenez said.
Valencia coach Unai Emery has not included Spain internationals David Silva and Pablo Hernandez in his squad for Saturday's match at home to Espanyol.
Silva damaged knee ligaments at the end of November and Hernandez has a muscle problem and neither have recovered in time, Emery said at a news conference.
Espanyol need to put behind them a difficult year that was marked by the tragic death of club captain Dani Jarque in August, midfielder Jose Callejon said.
"It has been a difficult year, and things have happened that have affected us a great deal and caused a lot of pain," Callejon told Espanyol's website.
"We have to focus on the positive, although at the same time we cannot forget the negative."
Deportivo La Coruna midfielder Juan Carlos Valeron does not understand
