Rob, 38, said online fraudsters had set up fake social media profiles to try to con money out of people touched by his plight.
He has been fundraising for charity since being diagnosed with MND nearly two years ago.
The dad-of-three was horrified after spotting a scam on Twitter begging supporters to donate to a phony PayPal account.
In a tweet, the former Leeds Rhinos star said: “Apparently there is a fake account copying my entire profile. They have been asking for people to send money to an email account.
“Please don’t be the one who falls for the scumbags.”
Wife Lindsey, 38, added: “It’s just shameful that somebody would try and capitalise on this and take money that is being raised for a good cause.”
Once dubbed the smallest player in the Super League, the 5ft 5in former England international was diagnosed with the terminal illness before Christmas 2019.
It causes muscles to waste away after a loss of nerve cells that control movement, speech and breathing. There is no effective treatment or cure and half the 1,500 people diagnosed each year in the UK die within two years. His plight was highlighted in a BBC documentary showing how MND is robbing him of his ability to walk and talk.
Physiotherapist Lindsey took part in the Great North Run at the weekend for MND research.
She added: “We acted on it straight away and reported it and the person who tweeted deleted it. Fortunately, it’s the first time we’ve come across anything like this. It’s quite unbelievable that somebody would try to do that.”
Rob and Lindsey, from Pontefract, West Yorks, have two daughters, Macy, nine, and Maya, six, and son Jackson, two.
Rob was awarded an MBE in the 2021 New Year’s Honours list for raising MND awareness.
They are supporting a Sunday Express crusade calling for £50million Government cash for an MND research facility and aim to raise £5million to build a specialist care centre in Leeds.