Newcastle can't recall the 18-year-old until January 16 under the terms of his current agreement.
But they want him back, and hope he will be the answer to their problems in front of goal.
Other than the freak 6-2 hammering of Norwich in October, The Toon have scored just nine goals in 12 Premier League games this season and sit a point above the drop zone.
Academy product Armstrong's only Premier League start for Newcastle came last December, and Coventry are keen to extend his loan until the end of the season.
But boss Tony Mowbray knows the young striker is in demand back at St James' Park after impressing for the Sky Blues.