The 21-year-old centre back is currently under contract to French third division side Troyes, where he won both the players' player of the year and the young player of the year awards last season.
Grayson added: "It was a good workout for us although I was disappointed with the first-half performance.
"We were very lethargic and didn't have much energy about us. I suppose we could excuse that with a hard session yesterday and travelling back from Belfast on Sunday.
"I was disappointed at how we were with and without the ball but in the second half we looked a far better team.
"We passed it around quickly, closed people down, and had the energy and desire that I expect from the team."
Grayson sent two teams out on Tuesday night, with Jermaine Beckford in action against his former club Wealdstone as part of the deal that took him to Elland Road.
Tresor Kandol, on his first pre-season appearance, scored his first Leeds goal in over a year but it could not prevent United going down to a 2-1 defeat.
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