The Cherries say the 21-year-old England midfielder will be out from six to nine months after rupturing his anterior cruciate ligament.
The Cherries youngster has been ruled out for six to nine months after rupturing his anterior cruciate ligament, the Cherries have confirmed on their official website.
The Bournemouth website announced the sad news on Thursday after further assessment and scans a day earlier revealed the extent of the damage to the 21-year-old's right knee.
Cook came through the ranks at Leeds, being promoted from the Under-18s to the senior squad in 2014 and going on to make 85 appearances for the Whites.
Since leaving for Bournemouth in 2016, he has gone from strength to strength in his 56 club appearances thus far and is deemed an important player for Eddie Howe's side.
Cook also captained England to the Under-20 World Cup title in 2017, becoming the first England captain to lift a world trophy since Bobby Moore in 1966.
Following the injury updates, some Cherries fans took to Twitter to express their sorrow and wish Cook well:
Devastating news, stay strong Lewis. Im sure Callum will be great support— Mel (@Melanha) 6 December 2018
That has literally ruined Christmas. Kids crying now. Thanks— samford (@samford_spencer) 6 December 2018
Gutted! A massive loss to us! You’ll Come back stronger @lewiscook_ keep your head up! Wish you all the best along with every other cherries fan! ⚽️— Emily Garsden (@EmilyGarsden_) 6 December 2018
Obviously devastating news for you @lewiscook_ Thoughts and best wishes with you. You will come back a stronger player, I know.— Lord William Snootsworth (@Snootsworth) 6 December 2018
When I saw you get up and flex your leg a bit it reminded me of when Cal did his at Stoke. I just thought God, I hope you haven't done the same. You did a little jog and I thought, he's OK! But....— Ian McD (@Mcdcrasher) 6 December 2018
Good luck with the rehab, it'll be tough, but you'll come back and be better.
Gutted for Lewis Cook! No better player than Wilson to have around d at this moment. Let's hope he's fit for the start of next season. Get well soon Cookie. #afcb— Tom palmer (@tpalmer77) 6 December 2018