That's the headline from this article in today's Financial Times. Apparently, Manchester United generated £173m in turnover while the Yankees generated $280m (£152m).
Of course, turnover can have little to do with profits, which to my mind would be a better measure for deciding which is the "world's richest sports franchise". My gut instinct tells me that Manchester United is easily more profitable. I suspect that United's wage bill is much lower than the Yankees', which is more than $150m. And, the Yankees minor league teams are probably more expensive than United's youth and reserve teams.