Robertson, out of the team as a precaution, watched from the stand as United beat Hibernian 1-0 in a pre-season friendly. But McNamara retains hope that the 20-year-old - who arrived 12 months ago from part-time football with Queen's Park - could still shun a move south of the border.
He said: "The clubs have agreed a fee. It's all down to Andrew and his family now, the decision he makes. He's obviously got to speak about his personal terms, where he sees him playing and his future. Selfishly, I hope he decides to stay another year.
"It's a fantastic story, what's happened to him - bids of crazy money, young player of the year, he's a Scotland regular now."
For United, yesterday's trip to the capital was the first chance to see summer signing Jaroslaw Fojut in action and he was joined in the starting ranks by fellow recruits Callum Morris and Blair Spittal, with Mario Bilate given his first start.
But it was a more familiar face who got the decisive goal 14 minutes from time after an error from Hibs' latest signing, Scott Allan.
The former United youngster misplaced a pass minutes after making his debut as a late substitute, and Aidan Connolly teed up Chris Erskine, who curled a finish into the far corner.
The shot beat Mark Oxley in the Hibs goal, on loan from Hull City, who is expected to be confirmed in the next 24 hours as the club's fourth summer recruit.