The Football League is set to make a decision on the 75 per cent takeover by Cellino in the next seven days through their Owners and Directors Test.
However, the Cagliari owner faces a conviction for tax evasion on Tuesday when a court in Italy will rule on allegations revolving around non-payment of import duty.
That could wreck the businessman's chances of taking over at Elland Road, but McDermott, who Cellino attempted to sack illegally in January, has given his support to the 57-year-old.
He told the Yorkshire Evening Post: "I have a view. I've got to say that he knows his football, Massimo.
"He knows what he wants and he's been nothing but supportive as far as I'm concerned. I'm grateful for that.
"We've had many conversations and he's been nothing but supportive.
"As far as I'm concerned, the next week will be an important one in our history. It's important that we get the right decision."