The player enjoyed a successful loan spell with United at the end of last season and is available on a free transfer following his release from Reading.
With Grayson in the market for a new centre-half, he is not ruling out a move for the 30-year-old.
He told the Yorkshire Evening Post: "He's another option for us. I think all along the summer Sam has been keeping his options to himself and we have as well. We've got to make sure we get the right ones for us.
"Sam did ever so well during his time here. Obviously it's something we will probably catch up on and now we've started back it's a case of seeing where he's at really."
Grayson will hand non-competitive debuts to Jason Crowe and Shane Higgs when Leeds travel to York for their opening friendly on Sunday.