Wilson limped out of the Premier League match at St Mary's in the 78th minute as the Magpies were well-beaten 2-0 by Ralph Hasenhuttl's Saints - who moved to the top of the table thanks to goals from Che Adams and Stuart Armstrong.
Bruce said: "It's a hamstring and we don't know how bad it is yet. He needs a scan.
"We'll not know how bad it is until we get him scanned. We hope that it's not too bad but we'll see."
When asked about Fraser's training injury which ruled him out of the Southampton clash, the Magpies boss added: "Unfortunately, yesterday he came into the treatment room and wasn't happy.
"We then scanned it and revealed a small tear. He won't make the internationals (for Scotland)."