Rayner suffered what is feared to be a suspected season-ending ACL injury in the second quarter of Monday's 28-point pre-season win over Gold Coast.

The 21-year-old collapsed in agony on the Metricon Stadium turf after landing awkwardly on his right knee, and will undergo scans later on Tuesday.

While gutted for the 2017 No.1 draft pick, Fagan is optimistic both player and club will take a positive approach to the disappointment.

"It will build his character ... I know he'll still continue to lead around our footy club," Fagan said.

"He'll try and find a way to make the most of this opportunity.

"They'll (teammates) be super disappointed for him, there's no doubt about that but in another way they'll probably be inspired to rise to another level hopefully.

"He is a good man, a very popular teammate.

"I know he'll be trying to find a way to influence the group."

In Rayner's absence the Lions overturned a 23-point halftime deficit to run over the Suns, scoring seven goals to none in the third term.

Key recruit Joe Daniher warmed up for the Lions' round one clash against Sydney with three goals while captain Dayne Zorko and Brownlow Medallist Lachie Neale were important in the second-half comeback.

Teenage schoolboy Harry Sharp also turned heads. The 18-year-old champion runner came into the midfield to replace Rayner and picked up 10 disposals, two clearances and a goal in an impressive display.

"His running ability really came to the forefront but also I thought he played with a lot of courage and attacked the footy," Fagan said.

"It was a pleasant surprise to see him do so well I must say.

"The plan was to give him a quarter at the end of the game but he ended up coming on for Cam so he got a bit more time than he bargained for."

Australian Associated Press