The 33-year-old was released on police bail on Friday night pending further inquiries into the crash in Winthorpe, near Newark, Nottinghamshire.
A 35-year-old man was airlifted to Nottingham's Queen's Medical Centre from the scene of the crash on the Lincoln-bound carriageway of the A46/A17 interchange.
A Porsche, a Volkswagen Polo and a Vauxhall Astra were involved in the incident at 2.50pm on Friday.
The road was closed for two-and-a-half hours following the crash, which also left other occupants of the cars suffering from whiplash injuries.
King, whose previous clubs include Watford, Middlesbrough and Coventry City, underwent knee surgery last month.
A spokesman for Birmingham City said: "We are aware of a road traffic accident involving our player and the matter is now being investigated by the police."
- Transport Accident