Warriors fullback Roger Tuivasa-Sheck believes he needs to improve in defence.

Warriors fullback Roger Tuivasa-Sheck has been ruled out for the season after scans on Monday confirmed he had ruptured the anterior cruciate ligament in his left knee.

Tuivasa-Sheck was injured in his side's win over the Bulldogs at Westpac Stadium in Wellington.

In just his seventh appearance for the club, the 22-year-old was forced off the field after only 16 minutes.

"Roger is absolutely shattered and so is everyone around the club," said Warriors head coach Andrew McFadden.

"We had huge expectations about what he would bring to us this season and he was so excited about the role he had to play. He had settled in well developing his combinations and timing but now this. It’s the cruel side of football – we’ve certainly had more than our share of bad luck.

"Roger will have surgery in about three weeks and faces a long recovery but we’ll make sure he has plenty of support and care around him."