The former Reading manager is adamant that the 18-year-old midfielder will continue his development at Elland Road after impressing during a run in the first team
The 18-year-old central midfielder has featured seven times for the Championship outfit this season and caught the eye with a series of excellent performances.
Calm and composed on the ball and with an eye for a killer pass, Mowatt has featured in every minute of Leeds' last five fixtures, with McDermott hinting to Sky Sports that several Premier League clubs were keeping tabs on him.
But, when asked by Perform, the Leeds boss said Mowatt - who was called up to the England Under-19s squad on Wednesday - was not for sale, explaining: "I alluded to the fact that people are watching him. They can watch him as much they like, he's going nowhere as far as I'm concerned.
"His development will be at Leeds. He wants to play for Leeds. He's one of our own. He's an academy boy. He's a good lad and I think our fans really appreciate our own. I'm sure they appreciate Alex.
"His mentality is excellent. He can handle the ball, he'll take the ball even when we're under pressure and not playing particularly well. He's brave. He wants to get on the ball. It doesn't faze him.
"[Before] his first game against Doncaster, he just sat in the dressing room, didn't say anything to anyone, just went out and played like he did. He's going to be a good player."
Striker Matt Smith, who has scored three goals in the club's last two matches, enthused of his young team-mate: "Alex is very impressive and was involved with the first team from day one in pre-season.
"He is definitely someone that has stood out for me. I remember we played a pre-season friendly in Ireland and he really, really did stand out. It's testament to how good he is as a player, the fact that he is holding down a place so young, in such a competitive division at such a big club.
"Obviously there'll be a lot of people watching him because of his age. [His England call-up] is not a surprise at all. It's fully deserved and hopefully he can do well. We're going to have a top, top player on our hands, for sure."
Of their season as a whole, Smith added: "I think there's still the best to come, certainly. I don't think we have really got going, if I'm being perfectly honest.
"We've been guilty of being a little bit inconsistent but there have also been lots of positive signs. We're only six points off the play-offs and we haven't really been blown away by any means.
"Looking at the results that have gone against us, they've been by the odd goal and at times we've been guilty of our own misfortune, really. There's lots to work on to improve but, at the same time, we are upbeat and optimistic."