The players name came from a typo in the phrase "I wouldn't sign him unless...", where the writer typed "I wouldn't sign hi munless". Speculation then proliferated as to who this "Hi Munless" player was that the writer wouldn't sign.
Now used as a sarcastic response to an unlikely and wildly speculative transfer rumour on football internet forums - i.e. "why don't we sign Hi Munless while we're at it"
"is Hi Munless signing today"
"Could use him in a swap deal for Hi Munless"