The reaction of the Dutchman suggests it was a deliberate act but it appeared that Williams was only trying to hoof the ball away to clear any danger for his team.
However, Ferguson feels it was a dangerous deed and believes Williams should face the wrath of the Football Association.
"The Van Persie situation you can clearly see that he could have been killed," Ferguson said on Sky Sports News.
"The FA has got to look into it regardless that he has been given a yellow card. He should be banned for a long time because that was the most dangerous thing I've seen on a football field for many years.
"It was absolutely deliberate. The whistle has gone, the game has stopped and he has done that right in front of the referee, he could have killed the lad.
"It was a disgraceful act by the player, he should be banned for a long time."
Swansea managed to hold out for a 1-1 draw at the Liberty Stadium after Patrice Evra opened the scoring thanks to Michu's 13th goal of the season.