(By Paul Virgo) Rome, September 16 - Kakà said Monday he was suspending his own salary after adding to AC Milan's injury crisis with a thigh problem sustained at the weekend in his first competitive match since returning to AC Milan from Real Madrid. The Brazilian playmaker, who helped Milan win the 2004 Serie A title and the 2007 Champions League during his first stint at the club, is expected to be out for at least a month after getting hurt in Saturday's 2-2 draw at Torino. "I've decided to suspend my own salary in this period because I only want support and affection from Milan to be able to heal soon," Kakà said in a video message on the club's website. "I started the treatments today. Your affection at the moment charges me up and motivates me to return as soon as possible. "It's a tough, difficult time. I hope to be on the field as soon as possible". The 31-year-old has returned to Milan after struggling at Real, whom he joined in 2009 for 68.5 million euros, in part due to a spate of injuries. Milan coach Massimiliano Allegri faces a stiff challenge in preparing for his side's Champions League Group H opener at home against Celtic on Wednesday due to his squad's fitness situation. Midfielder Riccardo Montolivo also suffered a thigh injury against Torino and looks set to be out for three weeks and forward Stephan El Shaarawy is out after hurting a leg muscle in training. Allegri may be forced to use makeshift fullbacks given how shorthanded he is in defence, with Ignazio Abate, Mattia De Sciglio, Matías Silvestre, Daniele Bonera all unavailable. Striker Giampaolo Pazzini is in sick bay too and midfielder Andrea Poli is a doubt for the Celtic game after taking a knock Saturday. Luckily for seven-time European champions Milan, their opener does not look to be the toughest encounter they will have in Group H, which also features Ajax and the mighty Barcelona. Celtic can be feisty opponents and they beat Barcelona in the group stage last season, but the Scottish team's skill levels are low by Champions League standards and they lose much of their intensity away from home. Serie A champions Juventus kick their campaign off in Copenhagen on Tuesday. The Turin outfit, who were knocked out by eventual winners Bayern Munich in the quarter-finals last term, are seen by some as possible contenders following the arrival of Argentine striker Carlos Tezez in the close season. They are in Group B, which also includes Galatasaray and Real Madrid. Serie A leaders Napoli face a tough start, with last season's finalists Borussia Dortmund visiting the San Paolo Stadium on Wednesday. Rafa Benitez's side, who have lofty ambitions after some big transfer spending that landed Argentine forward Gonzalo Higuain among others, are in Group F along with Arsenal and Olympique Marseille.