Carnegie Hall today announced that conductor Michael Tilson Thomas has graciously agreed to step in for Yannick Nézet-Séguin, leading The Philadelphia Orchestra’s performance in Stern Auditorium / Perelman Stage this Friday, December 6 at 7:30 p.m.Mr. Nézet-Séguin has cancelled this appearance as well as concerts this week in Philadelphia on medical advice that he not travel for the next few weeks due to sinus-related problems. Pianist Hélène Grimaud is soloist for this performance; Brahms’s Piano Concerto No. 1 will replace the previously-announced Brahms’s Piano Concerto No. 2 at her request. The second half of the program, featuring Berlioz’s Symphonie fantastique, remains as announced.