Sunderland confirmed on Friday they had received a fine from the Premier League after it emerged Ji Dong-Won, who moved to Augsburg on loan in January and will join Borussia Dortmund in the close-season, featured for the club this term despite not having international clearance.
The club admitted the offence blaming an "administrative issue" for the faux pas, and Sunderland consider the matter closed.
But Bruce - who brought Ji to the Stadium of Light in June 2011 - believes the club may face further punishment.
"That's pretty bizarre stuff that it's only surfaced now and he's played in four games," he said. "They should be in serious trouble, I would have thought."
Asked whether Sunderland should be docked points, he added: "It's the first I have heard of it and it will be interesting, I would have thought so though."
Meanwhile, Bruce insists Hull will "vigorously defend" striker Yannick Sagbo over his Football Association (FA) charge for improper conduct, for a social media posting in relation to the 'quenelle' gesture.
The salute - which is said to have anti-Semitic connotations - gained notoriety when Nicolas Anelka used it to celebrate a goal in West Brom's 3-3 draw at West Ham in December.
Bruce apologised if Sagbo's actions caused offence, and insisted it was not his intention to do so.
He added: "It's something that we have been made aware of for weeks, it's something that they have took their time over, the FA, to study it.
"We are going to defend him vigorously because we don't think Yannick has tried to offend anybody.
"Whether his actions have offended anybody, then on behalf of the club I will apologise.
"It's a reminder to every player about social media. I don't think there is any callousness at all in what Yannick has done but obviously the FA has seen it that he has done enough to offend people."
