Aretha Franklin announced Saturday that she would be unable to perform at Whitney Houston's funeral
due to leg spasms.
"Regretfully, I am so sorry that I was unable to be with you at Whitney's service today," the Queen of Soul said in a statement.
"I had every intention of being there. But unfortunately I had terrible leg spasms and locked leg muscles until 4:00 a.m. this morning following my concert last night, which I've been having for the last few days." (The singer acknowledged her uncomfortable footwear during her Friday concert.)
"I feel it necessary and very important to stay off my leg today as much as possible until concert time this evening. My heart goes out to my dear friend Cissy, Dionne, Bobbi Kristina and the rest of the family. May God keep them all. – Aretha & the Franklin Family."
On Friday night, the singer brought fans to their feet with a powerful show at Radio City Music Hall with old favorites, new songs, and a tribute to her late goddaughter.
"I would like to acknowledge the passing of one of the greatest singers that ever stood behind a microphone," Franklin told the star-studded crowd (Clive Davis, L.A. Reid and Jesse Jackson were in attendance).
"She's moved on up just a little bit higher now. And we don't wonder where she is. One of the last songs she sung is 'Jesus Loves Me.' When God is for you, who can be against you? That's all that matters."
In an exclusive tribute
written for PEOPLE, Franklin called Houston "a true superstar."
"Remember the hits. Forget the misses," Franklin wrote. "Let us all applaud and remember Whitney for the beautiful, giving and caring young lady and the talented artist she was."
Still commemorating Houston through music at Saturday's New Hope Baptist Church ceremony in Newark, N.J.: Stevie Wonder, who's expected to sing his hit "Ribbon in the Sky," R. Kelly and Alicia Keys
The Associated Press will stream Whitney Houston's private funeral service Saturday at noon ET on its Livestream site
, which will be available on PEOPLE.com.