Defending champion Juan Martin del Potro has withdrawn from the Indian Wells Masters due to a knee injury.
Del Potro, who skipped January's Australian Open as he recovered from a fractured kneecap, made his 2019 debut at the Delray Beach Open, where the Argentine star lost in the quarter-finals.
The 30-year-old saved three championship points to upstage Roger Federer for his maiden Masters 1000 crown in Indian Wells 12 months ago but Del Potro will not be returning to defend his title.
"Hi everyone! I wanted to give all of you an update that after playing Delray Beach we had various consultations with different specialists, and we decided that I needed to do a regenerative therapy treatment on my knee," Del Potro said in a statement posted on Twitter.
"Unfortunately I will have to wait for several days before I can get back on court and train.
"I am very sorry that I will not be able to defend my title in Indian Wells. I was really looking forward to going back and playing in such a special place, but I have to wait two weeks to see if the treatment will be effective to allow me to play in Miami.
"Thank you for for all the support and messages, and I will make sure to keep everyone posted on my recovery the next couple of weeks."