Sheffield Wednesday say there are "outstanding legal issues" surrounding Steve Bruce's move to Newcastle United.
The club said they were "disappointed to learn via public statement" that the former Owls boss had joined the Magpies on a three-year deal.
Bruce quit Hillsborough earlier this week after just six months in charge, taking coaches Steve Agnew and Stephen Clemence with him.
In a statement, Wednesday said: "Regardless of the fact that the staff resigned from their positions with the Club on Monday, there remains outstanding legal issues to be resolved between the club and the staff and Newcastle United.
"The club is currently considering its position and taking the appropriate legal advice."