I don't really know how it works in practice, but my gut feeling is that it won't affect the general market.
Why? Well one big holding wants to sell. Reasons? Could be they are just trying to realise a profit. Maybe they need some cash. Maybe they have taken a negative view on the future prospects for the company they are selling. Either way, there is a buyer for an equally big stake. The buyer must have the view that there is more upside to come. There can be no manipulation here. One big well researched player takes a different view to another big well researched player.
I don't think this will pose a major threat to retail investors.
