ST KILDA has granted personal leave to captain Nick Riewoldt after the tragic passing of his younger sister Madeleine.

Madeleine Riewoldt endured a five-year battle with a rare blood disorder called aplastic anaemia that left her with the inability to produce new blood cells and platelets.

She had hundreds of blood transfusions and two bone marrow transplants throughout her fight before she passed away on Tuesday morning with her family by her side.

She was 26.

"We are so proud of Madeleine for fighting as long and hard as she did," the Riewoldt family said in a statement released by the club.

"This spirit is a testament to her strength, she inspired us and so many and will continue to do so.

"We are grateful for and cherish the 26 years we shared as a family and she will remain in our hearts always."

Richmond forward Jack Riewoldt will also be given all the time he needs away from the club to deal with the loss of his cousin.

St Kilda president Peter Summers said the Saints would do everything they could to support Riewoldt and his family, and asked for their privacy be respected. 

"The family were by Madeleine’s side when she passed and have asked me to convey how incredibly brave she has been and how strong her character was," Summers said.

"Many St Kilda people have gotten to know Madeleine over the years. In particular, she often visited the rooms after games, not only supporting Nick but as part of the Saints family.

"This is obviously an incredibly sad and tough time for Nick and his family and the club will be providing support in any way we can."

Riewoldt sent a tribute to Madeleine after the Saints' upset win over Fremantle in round 18 last year in which he kicked four goals.

“To my sister Madeleine, who’s in hospital, I love you very much,” Riewoldt said in an on-field interview.

"I can't wait to come in and see you. Keep going, you're the bravest person I know and I love you."

Madeleine and Nick appeared in a feature interview that aired during the Port Adelaide-Hawthorn Channel 7 broadcast last May.

Soon after, she received a bone marrow transplant from a compatible donor from France after tests showed Nick and their other brother Alex were not matches.

The Riewoldt family has asked for privacy during this time.

Madeleine's wishes were for greater awareness to the need for people to sign up to the Bone Marrow registry at www.abmdr.org.au and Australian Red Cross Blood donation at www.donateblood.com.au.