Barenboim is suffering from herniated discs and cervical myelopathy, a compression of a spinal nerve that can lead to weakness in the hands. According to a statement from the CSO, he is undergoing physical therapy in Berlin, where he is the music director of the Berlin State Opera.
Earlier this week, the orchestra announced that Andrew Davis, the music director of the Lyric Opera of Chicago, would replace Barenboim in the CSO's season-opening concerts this weekend. The CSO has also postponed a recording session with Barenboim and violinist Nikolaj Znaider that was scheduled for September 15 and 16.
Barenboim's next planned appearances with the CSO are October 21-24, when he is scheduled to play the piano in a program conducted by Antonio Pappano and give a solo recital; a week later, he is to lead a program featuring soprano Deborah Voigt. The CSO did not say whether he is expected to recover in time for those concerts.
Robertson completed a term as the music director of the Orchestre National de Lyon earlier this year, and is the music director designate of the St. Louis Symphony.