Highmore will line up against fellow Marist products Tom Green and Phil Davis in Sunday's round one clash between St Kilda and the Greater Western Sydney Giants.

The 23-year-old, who was taken with pick No.45 from the 2020 draft, received the call up after impressing Saints coach Brett Ratten in training and pre-season matches.

He'll feature in the backline alongside recruit Callum Wilkie with key Saints defenders Jarryn Geary, Ben Paton and James Frawley ruled out with injury.

"The College is very proud of all of their achievements and wishes all three players well for the game," a College release said.

Canberra's Jack Steele will lead the Saints out for the first time against his former club, with co-captain Geary breaking his leg during the pre-season.

Davis will return to the Giants after missing the back end of last season due to a knee injury, marking his first match since their round-10 win over Essendon. Green, on the other hand, only appeared in six matches in his debut campaign.

The AFL clash will be played in wet conditions as Sydney braces for another down pour, with 25 to 45 millimetres forecast to fall.