The teenage Australian international signed his first professional contract for United last year, but sitting on the substitutes' bench was the nearest he ever came to making a first-team appearance in the Premier League.
"There were no surprises," Troisi told the Evening Chronicle.
"He really didn't promise anything. He's going through some tough times at Newcastle and he wants to buy some fresh players." Troisi completed a successful two-match trial for Dutch side Roda JC in January, but the two clubs were unable to agree terms before Keegan replaced Sam Allardyce in the Newcastle United hot seat.
"When that was happening Sam Allardyce was released," he said. "But there are other clubs that I'm looking at in Europe.
"I'm not sure yet, but we'll just wait and see." Troisi made his Socceroos debut in a goalless friendly against Singapore as a left midfielder in March and is now targeting the Beijing Olympics to keep himself in the shop window for European clubs.
"Hopefully, I will get the call," he said.
"As long as I do what I've got to do and the Olyroos (Australia's U-23 team) keep performing. Hopefully, it's good enough."