Bournemouth defender Simon Francis will be out for between six and nine months after rupturing the anterior cruciate ligament in his right knee.
The 33-year-old club captain was carried off on a stretcher after suffering the injury in Wednesday's 5-0 defeat by Tottenham at Wembley.
Francis has made 20 appearances in all competitions this season.
"We are devastated to have lost Simon to a serious knee injury," said Cherries boss Eddie Howe.
"It is a huge blow for us to lose our captain and someone who has performed so well and consistently for the team over a long period of time.
"There is a long road ahead but Simon is a model professional who has a positive mindset and is surrounded by good people. I know he will leave no stone unturned in order to get back as soon as possible."
Francis sustained the injury as he twisted trying to challenge Spurs forward Son Heung-min shortly before half-time.
Earlier this month, Bournemouth midfielder Lewis Cook was also ruled out for up to nine months after rupturing the anterior cruciate ligament in his right knee.