Real Madrid's new 18-year-old signing Arda Guler has been sidelined after undergoing knee surgery, the LaLiga club said on Monday, making him the third player they have lost to a knee problem.Guler, who was signed by Real in July from Fenerbahce, returned home early from the club's pre-season tour in the United States due to the injury.The midfielder's surgery comes after Real lost goalkeeper Thibaut Courtois and defender Eder Militao to anterior cruciate ligament (ACL) injuries."Arda Guler has today undergone arthroscopic surgery on his right knee, performed under the supervision of Real Madrid's Medical Services," Real said in a statement."Guler will start his recovery programme in the coming days."Real Madrid beat Athletic Bilbao 2-0 in their opening LaLiga game over the weekend and will next play away at Almeria on Saturday.