McDermott's position as Leeds boss in doubt after going on holiday[GETTY]
McDermott is understood to have taken a break after attending the League Managers Association's awards dinner in London on Monday night.
Cellino, whose deal to buy 75 per cent of the club's shares was completed on April 8, temporarily closed the club's Thorp Arch training complex on Friday in a bid to ease running costs.
Who's managing this club? Brian. Where's Brian?
Massimo Cellino
But the Italian businessman appeared angry at the absence of McDermott and his coaching staff.
"I think at this moment the club is not managed by anybody," Cellino said.
"Who's managing this club? Brian. Where's Brian?
Cellino unhappy with McDermott's decision to go on holiday [GETTY]
"I send a letter to Brian - help us. He's on holiday to get some rest.
"He was tired I can understand. But why this kind of reaction?"
When asked what he said in his letter, Cellino added: "Just let me know what he's planning for pre-season.
"What he's thinking for the future. What's his plan? What are his ideas?
"Where are the people that we pay wages to every month gone?
"Who gave them the permission? Who organised that? He's the manager."
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