The 18-year-old has impressed in his nine appearances and almost scored his first goal for the club in their 2-1 win over Middlesbrough on Saturday.
"We are trying to sort out his contract as we speak at this moment in time so it is good news for everyone," McDermott told the club's official website.
"I thought he was unfortunate not to score a goal on Saturday.
"He has got goals in his locker, I have absolutely no doubt about that.
"Ross (McCormack) can score from free-kicks but so will Alex. I've seen him do it in training and for the younger teams."