Brett Gregory jokingly made the claim on Twitter ahead of last week's transfer deadline day, saying that if United signed a striker, he would get him inked onto his backside.
Of course, Jamaican international Donaldson agreed to a 12 month contract at Bramall Lane - and Twitter users were quick to remind Brett of his earlier pledge.
READ MORE: Clayton Donaldson arrives at Bramall LaneHe said: "On transfer deadline day, around 30 minutes before the deadline, I tweeted that if Sheffield United signed a striker before the deadline I would get him tattooed on my backside.
"I thought I was safe, until Clayton Donaldson signed. I was then inundated with messages about my earlier tweet."
A fellow Blade suggested that he should get the artwork done to raise cash for the LJS Foundation - the charity set up by Blades' ace Billy Sharp following the death of his son Luey - and so a campaign has been set up to raise £1,000 to pay for the tattoo.
The crowdfunding campaign has already hit more than £300 - meaning that Brett will have to get the words "Clayton Donaldson" tattooed on his bum after setting an initial fundraising target of £250.
And if the appeal reaches £1,000, he will go the whole hog and have the former Birmingham City striker's face plastered onto his skin.
He added: "Please get donating and sharing."
Tattoo artist Ben Smalley, the owner of Skin Candii in Woodhouse, has agreed to donate the tattoo.
Donaldson was unveiled as the Blades' 10th summer signing, joining Chris Wilder’s side for an undisclosed sum after scoring 33 times in 102 Championship starts for City.
To donate to the fundraising appeal visit https://www.gofundme.com/tattooed-for-ljs-foundation