The 71-year-old announced he was stepping down from his role as Manchester United manager this week.
Ferguson is due to have a hip replacement this summer, but his son Darren - who manages Peterborough United, insisted this was not a huge issue - he says it was just down to 'timing'.
"There's no problem with his health, contrary to what some people are saying," Ferguson jnr said.
"He's got a small hip operation but there's no difference to most 71-year-olds. It's not a health decision.
"Basically he feels he's gone out at the right time, he's left the club in a fantastic position and they've hired a very good manager to replace him."