Barcelona defender Andreu Fontas tore a ligament in his right knee during their King's Cup victory over Osasuna on Thursday, and will miss the visit of Real Betis on Sunday.
He joins long-term injury victims David Villa and Ibrahim Afellay in the treatment room, along with forward Pedro who suffered a hamstring strain in the same match.
On top of the injuries, Barca sold Brazilian defender Maxwell to Paris Saint-Germain during the week and Seydou Keita has departed to compete with Mali in the Africa Cup of Nations.
"I don't like signing players in January... we are going to rely heavily on the youth team," Guardiola told reporters in Pamplona. "I believe in them completely. They better prepare themselves."
Real hold a five-point lead over their arch-rivals in second place and can extend that gap on Saturday for 24 hours if they win at Real Mallorca.
Germany midfielder Sami Khedira is sidelined with twisted ankle ligaments while Argentina winger Angel di Maria is recovering from a thigh strain and is doubtful.
Third-placed Valencia host Real Sociedad on Saturday, and the visitors, 16th, arrive after letting slip a 3-0 advantage to lose 6-3 on aggregate to Real Mallorca in the King's Cup during the week.
"The team are in debt to the fans and they need to give them a lift again and soon," Sociedad President Jokin Aperribay said on a visit to their training ground. "We cannot accept what happened in Mallorca."
Sevilla's cup exit during the week and three straight defeats in La Liga have put the pressure on coach Marcelino and his players for the visit of Espanyol on Saturday.
Espanyol are level on points with Sevilla, but below them in eighth on goal difference, and travel without first-choice goalkeeper Cristian Alvarez who has torn a calf muscle.
Two sides expected to compete for top four finishes, Atletico Madrid in 11th place and Villarreal in 18th, meet at the Calderon on Sunday with new coaches looking for their first wins.
Atletico's Diego Simeone and Villarreal's Jose Molina, former team-mates at Atletico in the 1990s, drew their first games in charge last week.
Basement side Real Zaragoza, who host Getafe on Saturday, have strengthened their squad with striker Carlos Aranda and are close to completing a loan deal for Croatia midfielder Tomislav Dujmovic from Dynamo Moscow, the club said.
New coach Manolo Jimenez, on his home debut, is seeking to end a run of 12 matches without a win in all competitions.
