Arbeloa has enjoyed an extended run in the first team of late, and has made 16 La Liga appearances this term.
But he was replaced after 70 minutes of last weekend's 2-2 draw at rivals Atletico Madrid and has been unable to train due to a cracked patella.
A statement on the club's official website on Saturday read: "After tests carried out this morning Alvaro Arbeloa has been diagnosed with an avulsion of the lower (part) of the right patella."
Speaking ahead of Real's home fixture with Levante, Real head coach Carlo Ancelotti rued the loss of the former Liverpool man.
"Arbeloa couldn't train due to problems with his knee. He has to rest for a few days but it's bad news for us," he said.
"He is very important for us because of his personality and experience."
Ancelotti also said he will make a late check on centre-back Pepe, who has been suffering with stomach ache.
Real needed two injury-time goals from Alvaro Morata and Cristiano Ronaldo to secure a 3-2 victory over Sunday's opponents earlier in the season and Ancelotti is expecting another tough test at the Bernabeu.
"Levante did well in their last few matches," he continued. "We have to be patient and play with intensity because it won't be easy."
