Gillespie comes off contarct at Well today and will join Newcastle in a Bosman deal.
It will mean a return to Tyneside for the former Toon academy graduate.
Bruce revealed today: "He's signed, and will be part of the squad next year; he's obviously not allowed to play now.
"With Rob Elliot leaving, it's important we have three goalkeepers. We've now got to make the call on (Freddie) Woodman at Swansea."