MUMBAI: The music launch of Amitabh Bachchan's forthcoming film 'Shamitabh' will be held 20 January. But the megastar says he is having nightmares over performing the 'Piddly' song at the event.

The launch event will be concurrent with the felicitation ceremony of music maestro Ilayaraja who has composed music for over 1000 movies.

The 72-year-old star has lent his voice for the song, which is composed by Ilayaraja, in the R. Balki film.

"And now on to the next event the evening to celebrate the 1000th film mark for the maestro Ilayaraja- and his connect with our film #shamitabhMovie...it shall be on the 20th and shall be a most striking evening...

"The prominent music directors and singers in tribute to the great man, and the release of the music of #shamitabhMovie...and…the worst part of the evening...me...having to sing live for the event on the 'Piddly' song... nightmares have begun!!!," Big B posted on his blog srbachchan.tumblr.com.

This is not the first time Ilayaraja has teamed up with R. Balki. He worked with Balki in 'Cheeni Kum' and 'Paa' as well.

Meanwhile, the screen icon kick started promotions for 'Shamitabh' with hordes of fans in the packed by lanes of Ahmedabad. The movie stars southern superstar Dhanush and marks the debut of Kamal Haasan's daughter Akshara Haasan. The film is set to release 6 February.