Crusaders loose forward Tom Sanders could miss the first seven games of next season with an ankle injury.

Crusaders flanker Tom Sanders has joined an already lengthy injury list as the defending champions continue to lose players at an alarming rate.

A day after No 8 Kieran Read was ruled out for about four months with a back injury, the Crusaders confirmed Sanders would miss up to four months with an acute ankle fracture.

Sanders, who has moved home to play for the Crusaders after playing for the Chiefs the past two years, sustained the injury during pre-season training and has had surgery.

GETTY IMAGES Crusaders No 8 Kieran Read is out for about four months with a back injury.

"The Crusaders' medical team will monitor his recovery, with an anticipated recovery time of approximately 3-4 months," a statement released by the team said.

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Should Sanders miss four months, like Read, he would miss the Crusaders' first seven games of 2018, possibly returning for their match against the Sunwolves in Christchurch on April 21.

The Crusaders plan to call in injury cover and will announce a replacement in due course.

Read goes under the knife on Saturday to have a prolapsed lumbar disc in his back fixed.

Sanders' injury won't have gone down well with head coach Scott Robertson, who is already set to go without All Blacks props Joe Moody (shoulder) and Owen Franks (Achilles) until as late as May.

In addition to Read and Sanders being out, loose forward Jordan Taufua (broken arm) isn't training but should be available come their season opener against the Chiefs in Christchurch on February 24.

Fullback Israel Dagg missed the northern tour with the knee injury he is still recovering from, but he is also expected to be available when the new season kicks off.

Halfback Ere Enari (broken leg) has already been ruled out of the 2018 season and was replaced by Canterbury halfback Jack Stratton in the squad.

Pivot Richie Mo'unga, fresh off a stellar year with the Crusaders and Canterbury, is recovering from his second broken hand this year.

In addition to Taufua, Robertson still has Pete Samu and rookie Ethan Blackadder available to play in the No 6 jersey. Lock Scott Barrett can also play on the blindside.

Sanders, a key part of Canterbury's Mitre 10 Cup winning team the past three years, made 13 appearances for the Chiefs the past two years and can play both flanker and No 8.