Hagen made well over 100 appearances for the club between 1995 and 2000, having previously played for Rangers and Hearts.
Hagen left Brockville in 2000 as a fan favourite, going on to play for Livingston, Clyde and Peterhead before retiring at Bo’ness United.
Falkirk announced in a club statement that Hagen was suffering from motor neurone disease, as had been rumoured online.
“The club is aware of rumours that have arisen on social media regarding the health of former Falkirk player David Hagen,” their statement read.
“To prevent further speculation and further attempts by the media to visit him at home, the club can confirm he has very recently been diagnosed with motor neurone disease.
“The club is providing to David and his family our fullest support and would ask that their privacy is respected during this difficult time.”
Hagen is just 45 years old, having retired in 2007.