Leeds United sensation has picked up an injury while on international duty.
The talented teenager sustained an ankle injury while with England's under-19 squad, the BBC reported.
Cook has been an integral part of the Leeds side this season, and his international recognition appears to have come at a price.
The Yorkshire Evening Post reports he has been sent for scans amid fears he has ankle ligament damage.
That would see Cook ruled out for around three weeks minimum, but could be longer if there are complications.
For Leeds there are benefits though to the news. It gives them a chance to rest Cook, having played in 38 games this season already, and take a vital breather.
It also can act to calm any intensifying speculation regarding his future by taking him out of the spotlight, while players on the fringes of the first team will have extra chances to prove themselves capable of stepping up.
His injury has drawn a mixed reaction from fans, here is a look at a selection via Twitter...
Whilst Cook having an injury is not helpful the rest he will get between now and pre-season training will do him good. #lufc— Michael (@MGlufc) March 31, 2015
I wouldn't mind seeing Dawson given a chance on Saturday if Cook is injured. #lufc— Graham Coulson (@grahamcoulson68) March 31, 2015
Cook has a whole season at Leeds playing the second most games&most for outfield player, goes to England for a week ends up injured#lufc— Ryan Pinnick (@RyanPinnicklufc) March 31, 2015
Cook injured. On the bright side, might stop him being sold this summer #lufc— James Steiner (@jamiemsteiner) March 31, 2015
Cook injury is a cunning ploy from NR to avoid offers in the summer... "He's injured, honestly!" #lufc— Liam Pháidí Joe (@ismiseliam) March 31, 2015
If Lewis Cook has ligament damage surely this means we HAVE to recall Michael Tonge!? I long to see him on Elland Road turf once more #lufc— Daniel Howard (@DanielHoward92) March 31, 2015