How far does a remake legally have to differ from the original source?

[sunniray]

So I have a buddy who made a song to a beat that was used by a commercial artist and the song itself is getting alot of attention. He wants to take it further but I fear that down the line he will have problems with it being a used "industry" beat.
I offered to make a similar beat that can work around his song, but be close to the original beat he used. I need to know legally how far do I have to take the song away from the original to prevent issues later on.
Also the beat he used is very, VERY simple... Standard bounce drum pattern, about a 7 note melody and a 1 word sample.

 

[Visceral]

Worst case scenariois that he will have to pay royalties... oh no wait, worse case scenario is HE GETS SUEEEEEEED!

My theory is that if programs like SHAZAM can't pick it up then it is good for non-commercialized music..... if it's commercialized then it will have to be undetectable by the human brain, so no one can tell.

if it gets big then just edit the sample so it sounds different or replace it.