The 18-year-old has made 19 appearances for the Magpies since his debut during the 2013-14 season at the age of 16.
"We've got one striker and the search goes on," Sky Blues boss Tony Mowbray told BBC Coventry & Warwickshire.
"We're working very hard for that. It's about being patient and waiting to get the right one. We might have to wait until a week or two into the season."
Mowbray added: "That's when Premier League clubs decide on their 25-man squads and there are players who are not in it, even though they've done the whole of pre-season. We're looking for players that can bring some dynamic movement, who can burst though, be powerful and run in behind and we're think they're coming.
"Adam Armstrong is a striker we've been tracking throughout the summer and a prospect we're really excited by. He has a fantastic eye for goal and his movement in the area makes life difficult for defenders. It is an important stage of his development and he needs first-team games to progress as a player so this is a big chance for him in his career."
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