Leeds have lost seven of their last eight matches as the saga over the Italian businessman's proposed takeover has unfolded, a saga which means the players have still not been paid their March wages in full.
McDermott - sacked on Cellino's say-so at the start of February only to be reinstated - has repeatedly cited the uncertainty over the club's future as a mitigating factor in results.
But the Football League could ratify the change of ownership at a board meeting on Thursday after its initial decision to block the takeover was overturned by an independent QC.
And, speaking to Sky Sports News' Bryan Swanson, Cellino said the way is now clear for McDermott to prove he has what it takes to manage the club.
Asked whether McDermott would remain in charge he said: "Why should I fire him to waste money? I think he has to show that he's a good manager.
"I've heard he had a lot of problems with the team, with the market, but now we solve the problems.
"We're going to pay the wages, he's got a chairman - Massimo Cellino representing an Italian company. It's not a ghost bank or a ghost company in Saudi Arabia or wherever else. So that's it.
"I heard before every game how 'we've got a problem, there's no company, we don't have a chairman...' Okay, let's play now, let's see tomorrow, let's start a new game.
"I hope that Brian is going to do his job good. I'm going to give him (sic) if it's good for the team."
Pressed on whether the players would now receive the outstanding balance on their wages he said: "I think the players will be paid, but I think it's more important to pay the employees than the players sometimes.
"But I don't think it's a big problem."