Wallabies back Christian Lealiifano has been diagnosed with leukaemia and is undergoing treatment in hospital, his ACT Brumbies club said on Saturday.

Lealiifano, who has played 19 Tests for Australia and 117 Super Rugby games for the Brumbies, was diagnosed with the cancer that affects the blood and bone marrow following a brief illness.

The Brumbies released a statement after first contacting all their players, coaches and staff about the diagnosis of the 28-year-old inside back.

"At the moment it's just a matter of ensuring Christian receives the best care and support he can at this time," Brumbies interim chief executive Phil Thomson said.

"He is one of the most respected players within this group and this news has come as a huge shock to all of our players, coaches and staff.

"Everyone knows that Christian is an amazing young man, an important member of this team and of the Canberra community.

"Our thoughts and prayers are with Christian and his family at this time."

Australian Rugby Union chief executive Bill Pulver said the national body would do whatever they could to support the player and his family.

"We were shocked to receive the news of Christian's diagnosis yesterday and our thoughts are firmly with him as he begins his treatment," Pulver said from Rio de Janeiro where he is attending the debut of the Olympic rugby sevens tournament.

"Anyone who has ever had any involvement with Christian knows he is an outstanding young man, as well as being an exceptionally talented rugby player."

Wallabies and Brumbies team-mate David Pocock said through social media that he was "still coming to terms with the news".

"Really tough 24 hours trying to come to terms with news about Christian. One of the most respected and loved players I've played alongside," Pocock tweeted.

"I know he'll be strong through this and Brumbies family will be supporting him and his family however we can."

Lealiifano's former coach, Andy Friend, also tweeted his support from the Rio Olympics.

"Just finished marching in opening ceremony and received the news on @CLealiifano," he wrote from Rio.

"My night doesn't feel so special anymore. Get well Bruz..."

New Zealand-born Lealiifano and his partner, Luga, only in June celebrated the birth of their son Jeremih.

"It's so special and it's hard to describe. Everyone says it's the best feeling, and it is," Lealiifano said at the time of the birth.

"But you can't describe it, it's unreal to bring another life into this world and it's a massive blessing."

Source: AFP