The Black Cats' first choice will miss the start of the Premier League season after breaking his arm for the second time in eight months last week.
The injury comes as a blow to Bruce, who has seen his keeper's time at the Stadium of Light punctuated by a catalogue of fitness problems.
And the absence of Gordon from their curtain raiser with Birmingham on 14th August has left the boss reeling.
Bruce, currently in Portugal with his players for a pre-season training camp, told the club's official website: "It was devastating - a complete freak accident.
"It happened just when we had Craig at the top of his game and he will be a big miss for us.
"It's a big blow, but we will have to get over it. Every club has its knocks over the season. Craig needs a bit of luck and we wish him well."
The injury to the 27-year-old leaves Bruce with a gap to plug in the short term and it remains unclear whether he will make an unplanned dip into the transfer market.
Bruce already has three other shot-stoppers on his books in the form of rookie Trevor Carson, new recruit Simon Mignolet and Marton Fulop.
Fulop's future is unclear after rumours suggested the Hungarian would leave Wearside in the summer but Bruce is confident his back-up keepers can provide sufficient cover.
He added: "We have got plenty of competition.
"Young Simon has come in and Trevor has played in pre-season and done very well, plus there is Marton Fulop, who is with us for the time being."