Docherty, who led United for five years in the 1970s, told Sky Sports News: "I think it's fantastic business. It was £40million, it was £50million, it was 60, now it's 80 and I think they should cut their hands off and run and don't even consider about it at all."
"I can only think Alex has come to the conclusion - and I think he's quite right - get rid of him because the same problem is going to arise next year again and the year after.
"And I sit at home giggling sometimes when managers say 'he is not available at any price' and a fortnight later he is gone.
"Every player has got a price and if a club is prepared to pay that price then he will go.
"When you fall out with Sir Alex, whatever may be the reasons - Beckham did it as well with the entourage he carried with him - they're on their way.
"You can't have this disharmony brought upon the players and the club every year and I think United - £80million - cut their hands off and give Real Madrid the problem of handling Ronaldo from now on in."
The Glasgow-born former United boss also believes there have been strains between Ferguson, Ronaldo and the player's agent Jorge Mendes.
"I think he (Ronaldo) has fallen out with him (Ferguson) once or twice," Docherty continued.
"Not Sir Alex's fault I might add, I think the problem (is) between Ronaldo and his agent Mendes that (leads to a) fall-out.
"It's every year; he's staying, he's going, he's coming, he's happy, he's not happy. You can't have that every year.