The pacy winger has not played since returning injured from international duty in March, when he scored in World Cup qualifiers against Israel and the Faroe Islands.
Newcastle are preparing for their final two games of the Premier League season – home to Sheffield United on Wednesday evening before a trip to Fulham on Sunday – but Fraser is not expected to feature in either game after only just resuming training.
The 27-year-old has had an injury-interrupted season since joining the Magpies on a free transfer following his departure from Bournemouth last summer, and Bruce believes it would be a risk for Scotland boss Steve Clarke to include him in his 26-man Euros squad, which is named tomorrow ahead of warm-up matches against Luxembourg and the Netherlands in Portugal.
Bruce said: "It has been a difficult time for him. He does desperately need a pre-season. Pre-season is huge for him.
"Whether he's going to be picked in the Scotland squad, I would think that would be a gamble too since he's missed the last six, seven weeks playing no real football or training.
"With the problems Scotland have got and 26 players, I don't know, but it's certainly a gamble."
Scotland kick-off their Euros campaign against Czech Republic on June 14 at Hampden, followed by matches against England at Wembley on June 18 and Croatia at Hampden on June 22.