The 26-year old, who will require surgery in the next few weeks to fix the left knee problem, sustained the freak injury during a routine passing drill.
Grant, who was the unfortunate recipient of the same injury in 2013 but to the opposite knee, is remaining positive.
"It's disappointing but I'll be alright,” said the Canowindra born defender.
"These things happen in football and it has happened to me before so I know what it takes to recover and come back stronger.
"I'm looking forward to getting the surgery and beginning the hard work to get back before the end of the season,” he continued.
"The boys have been really supportive and I'm still going to be part of the group every day, as we look to defend our titles."
Head Coach Graham Arnold expressed his disappointment for the Sky Blues current longest serving player.
"Obviously it's a blow and it’s devastating for the kid,” he said.
“He was fantastic for us last season and we will give him the best medical support he needs to recover fully.
“We are fortunate that we have excellent cover in Aaron Calver, Seb Ryall, Paulo Retre and Josh Brillante.
“However we will definitely be looking at an injury replacement.
“We know the type of professional Rhyan is and we expect him to be available for the last few games of the season, the Finals Series and the ACL.”
Grant has played 146 Hyundai A-League games for the Sky Blues, scoring seven goals including the equaliser in last season’s Grand Final.
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