The setback comes at an inopportune time as coach Manuel Pellegrini looks to build on Real's positive display against leaders Barcelona at the Nou Camp on Sunday, when they were unfortunate to lose 1-0.
Barca are now five points clear at the top, having extended their lead with a midweek defeat of Xerez, in a game re-scheduled because of the Club World Cup.
"He has been playing through the pain. He has had a groin problem and this perhaps explains his inconsistent performances," Real sports director Miguel Pardeza told Radio Marca.
"In my day it nearly always required an operation but now there are other types of treatments which are much better, and I am sure he will be back with us again very soon."
Substitute Zlatan Ibrahimovic's superb last-minute strike made the scoreline more respectable at 2-0 and ended a run of three consecutive away draws.
Guardiola admitted it had been a far from vintage performance although understandable so soon after the 'clasico.'
"This was a very dangerous game for us right until the end," he said.
"We became bogged down, we didn't move the ball about cleanly, and we were too slow. It's clear we weren't at our best."
