King made over 100 appearances for Chesterfield across three years, contributing to their promotion to the EFL last season, before leaving in the summer.
The well-liked defender became a free agent but later signed with Swindon Town in League Two and faced his former club, Chesterfield, in the opening match of the new season.
The 28-year-old had started all six league matches for the Robins before their 2-1 loss to Port Vale last Saturday, which placed them 21st in the standings.
Jeff King won promotion with Chesterfield last season.
When the team news was released, Swindon fans were questioning why King wasn’t included, but the club later shared the tragic news.
They tweeted: “#STFC’s Jeff King was absent from today’s matchday squad as his mother sadly passed away this week. Our thoughts are with Jeff and his family at this difficult time.”
Chesterfield fans have been sending ‘Kingy’ their best wishes with hundreds of supporters leaving messages of support for him.