The injury wasn't obvious at the time but it was announced by Saracens on Wednesday that Wray will be seeing a consultant this week.
The 31-year-old came on as a half-time replacement for Billy Vunipola at the Gardens and helped Saracens to beat Saints 30-6 in the Gallagher Premiership encounter.
Ferguson only heard the news of Wray's injury on Wednesday morning.
And at the media session later that day, Ferguson said: "I read about it and it sounds horrific.
"He's a really good guy.
"We were aware something pretty serious was going on in the tunnel because I think it happened post-game in that he'd finished playing and there was a collapse or he felt rough once the game finished.
"First and foremost we wish him a speedy recovery because a fractured skull sounds horrific, but I only know what I've read online about that."