Usher's 11-year-old stepson Kyle Glover was reportedly declared brain dead when hospitalised after the weekend crash.
Glover and an unidentified girl were injured as they sat in an inner tube being pulled by a boat which was struck by the jet ski. A friend family is believed to be under investigation over the matter.
The 'Scream' singer was due to present an award at the 20th annual ESPY Awards this evening, but will not appear in order to focus on his family's well-being, reports Page Six.
New Girl's Zooey Deschanel and model Bar Refaeli are expected to honour the best in sports at tonight's awards show.
Rob Riggle hosts the ESPY Awards, airing at 9pm ET on ESPN.