The collision took place at around 12.20am yesterday morning, when a silver Kia Ceed travelling along the entry slip road to join the M1 northbound at junction 31, Sheffield was involved in a collision with a pedestrian thought to have been in the road.
A South Yorkshire Police spokesman said: "The pedestrian, a 23-year-old man, was taken to hospital where he currently remains with serious and potentially life-threatening injuries.
"The driver of the Kia, a 19-year-old woman, was not injured.
"Officers investigating the collision want to hear from anyone who saw what happened or who thinks they may have seen the pedestrian prior to the collision occurring.
"If you can help, please call 101 quoting incident number 16 of December 9, 2017."