Stone said Newcastle's salary cap was ''getting pretty tight at the moment'' but he still hoped to sign another ''one or two'' more players.
One of those is likely to be 35-year-old Adam MacDougall, whose manager has been negotiating with the Knights for a deal next season.
''He's very keen to stay here, we're very keen to have him, so I expect we'll come to some conclusion,'' Burraston said.
If MacDougall were retained, Stone indicated it was unlikely the Knights would continue talks with another veteran centre, Matt Gidley, who has been with St Helens for the past four seasons.
''I'd suggest it wouldn't be a probability of having them both in the same place at the same time,'' Stone said. ''I'm not saying it would be out of the question, but I'd say it would be doubtful.'