The Rock is the latest celebrity to back a campaign to find a six-year-old boy a bone marrow transplant.
Marley Nicholls, from Newport, has been diagnosed with aplastic anaemia, a rare condition which stops the body producing enough blood cells.
Thousands have signed up to become potential stem cell donors since a campaign was launched, Marley's mother Shaney Truman said.
Dwayne Johnson tweeted his support, saying he was "pullin' for Marley".
The 46-year-old was the second highest-paid actor in Hollywood in 2018, pulling in earnings of $119m (£92m) in the past 12 months.
His move into acting followed a highly successful career in WWE.
The family have been searching for a suitable donor since Marley was diagnosed earlier this year with the condition, which affects between 30 and 40 children each year in the UK.
Man I hope this little boy here in the UK finds a bone marrow match. Pullin’ for you Marley! DJ https://t.co/Np2i8WbvWR— Dwayne Johnson (@TheRock) October 25, 2018
Their biggest hope of a suitable donor was Marley's brother, but George was found not to be a match.
Other celebrities to throw their weight behind the campaign includes Heidi Klum, Vernon Kay, Keith Lemon and Beyonce's mother Tina Knowles.
Their parents launched the Marrow for Marley campaign on Facebook, calling on people to add their names to a register to become a stem cell donor.
Ms Truman said 14,000 people had signed up to become potential stem cell donors since the campaign was launched.