The 27-year-old England international was punished on Tuesday evening following a disciplinary tribunal.
The incident happened on Sunday during Huddersfield's 17-16 defeat to the Saints in the fourth round of the Challenge Cup.
"I would never intentionally put someone in a position that could potentially injure them," Ferres tweeted.
"There was no intent or malice in the tackle and I am glad that Jonny is okay. I have accepted my punishment and hopefully we won't see any more incidents in the game like this."
Ferres was also fined £300 for the incident.