Carnegie released a statement concerning the delay last week; a spokesperson for the hall subsequently confirmed that the score is not yet finished. (Knussen is a genial and widely liked figure in contemporary music circles — as composer, conductor and public spokesperson — but he does have a longstanding reputation for not completing his commissions on time.)

To replace the concerto on the April 13 program, Serkin will play Olivier Messiaen's suite for piano Oiseaux exotiques. And the concert will still include a Knussen premiere: the first new York performance of his Requiem — Songs for Sue. The composer wrote the work, a four-song cycle for soprano and chamber orchestra, in memory of his wife, a music educator and television producer who died in 2003. The score received its world premiere in Chicago in April of last year; three weeks later (as it happens), nearby Northwestern University awarded him the Nemmers Prize in Music Composition, worth $100,000.

The evening also includes Magnus Lindberg's Corrente and Julian Anderson's Book of Hours. Susan Narucki will be the soprano soloist, and Knussen will conduct The Zankel Band.

The concert begins at 7:30 p.m. on Tuesday, April 13 in Carnegie's Zankel Hall. Information and tickets are available at www.carnegiehall.org.