AFL.com.au understands Johnston's management has entered the earliest of preliminary talks with the Crows, who remain undecided whether the 23-year-old's stay at West Lakes will be extended.
Johnston is only contracted until October.
A brilliant set shot at goal, last season Johnston told AFL.com.au he was most proud of his defensive development in 2013.
The Crows are light on for key defenders, with the imminent retirement of Ben Rutten and Andy Otten's knee injury.
Surgery to remain a damaged tendon in his hand sidelined Johnston for 13 weeks this year, but he transitioned into defence upon his return to the SANFL.
Johnston had just one goal kicked on him in the club's 65-point, round-18 loss to Norwood.
He managed 20 disposals, seven inside-50s and two goals in round 16 and the next round had 22 possessions, four inside 50s and one goal.
Asked about his switch to defence after Adelaide's seven-point loss to North Melbourne on Saturday, Crows coach Brenton Sanderson said Johnston had the versatility to play both forward and back.
"This time of year we have to look at guys playing different roles," Sanderson said.
"He's one option that can definitely play as a third tall defender for us.
"We do need some other options and he can play forward and back."
Johnston has been dogged by injury since being selected by the Sydney Swans with pick No.12 at the 2008 NAB AFL Draft.
The 13 weeks he missed this year followed 13 last year because of a broken leg and ankle injury.
His first season with the Swans was written off after having a bone removed from his foot and he missed a further 14 weeks in 2011 due to a reoccurring ankle injury.
