Police confirmed on Monday that a 35-year-old male pedestrian had been involved in a collision with a lorry on the A64 near Bishopthorpe, York, leaving him with serious injuries and needing to be airlifted to hospital.
Reports in the British media have linked Carlisle - who turned 35 in October - to the incident, while police have issued an appeal for witnesses.
Carlisle's career included spells with Burnley – who he helped clinch promotion to the Premier League – his hometown club Preston North End, QPR, Blackpool, Watford and Leeds United before he hung up his boots at Northampton Town last year.
He has most recently been working as a pundit and the Football Association were joined by a host of Carlisle's former clubs in wishing him well.
The Football Association posted on Twitter: "The thoughts and prayers of all at The FA are with Clarke Carlisle and his family at this sad time."
Burnley echoed those sentiments, tweeting: "The thoughts of all at Burnley Football Club are with Clarke Carlisle and his family."
Northampton added: "Clarke is an inspiration and a fighter and we are sure all Cobblers fans will join us in wishing him well."