Säpo and the prosecutor's national security unit prosecutor (Åklagarkammaren för säkerhetsmål) are jointly looking at whether Sverker Göranson's statements to the Svenska Dagbladet (SvD) newspaper at the beginning of the year put Sweden at risk.
"Talking about national defence is of course extremely sensitive," the unit's chief prosecutor Tomas Lindstrand told the Dagens Nyheter (DN) newspaper on Friday.
"The follow-up question is how well-known the information already was and how detailed it was, but of course that kind of information could be very useful to a foreign power, especially when it comes from the commander-in-chief."
Lindstrand said that if the investigation goes ahead, it would lie in the hands of the Justice Chancellor (Justitiekanslern) as the information was printed in an interview and has freedom of the press implications.
Göranson himself denies having revealed classified information. He told DN a few days ago that anyone could have come to the same conclusion looking at publicly available statistics about Swedish military capacity.
He has since gone on sick leave for exhaustion.
His statements in the run-up to the annual defence conference in Sälen, organized by the think tank Society and Defence (Folk och försvar), caused a stir in Sweden and beyond.
It rattled the cages of Swedes who remain faithful to the country's centuries-old tradition of neutrality and of those who would like to join Nato alike.
The Nato chief Anders Fogh Rasmussen, who also attended the conference in Sälen, applauded Swedish contributions to Nato efforts but underlined that the military alliance had no obligation to come to Sweden's defence in case of war.