The stars are in mourning after discovering The Black Eyed Peas' ex-manager Nick Lauher - who guided the band to success - died from a suspected prescription drug overdose last week.
A source said: "Will.i.am has been left utterly devastated.
"He worked with Nick for a long time and had become close friends over the years."
Cheryl grew to know Nick when will.i.am managed her solo career from 2011, and she will drop her plans to fly to San Diego, California, next week ahead of the funeral.
The source told The Sun newspaper: "Cheryl grew to know Nick well due to her friendship with Will.
"She has cleared her diary to go to San Diego. She wants to be there to support Will."
Meanwhile, will.i.am's bandmate Fergie has also been left feeling distraught following the news and she will also fly from Los Angeles to the ceremony, which is taking place in the city where Nick grew up.
She took to Twitter earlier this week to pay her respects, writing: "R.I.P. @NickLauher, my friend. Truly one of the sweetest guys I've ever met. #heavencouldntwaitforyou #angel #love #BEPfamily (sic)."