The 38-year-old, who came out of retirement in 2012 having decided to hang up his boots at the end of the 2010-11 season, has not featured for United in recent months.
Robson told PA: "Giggsy has got another year, but he looks as fit as he was when he was 21. Scholesy I'm not so sure about. He's been having a few problems with his knee. So I think he might just call it a day."
Ryan Giggs, however, recently signed a one-year extension to his contract.