West Midlands Police is being investigated after a man threw himself in front of a tram moments after officers dropped him off at a Midland Metro station.
The Independent Police Complaints Commission will carry out an inquiry into yesterday's incident, which left the man fighting for his life in hospital last night.
The man, who has not been named, was picked up by officers in Smethwick and later dropped off at the Handsworth Booth Street station.
Officers said they had been called to help the man by a member of the public but insisted he was not involved in an incident, was not arrested and had not been in custody before the accident.
Chief Inspector Sue Southern, of West Midlands Police, said last night: "We can confirm that police officers were assisting a man this morning and he was given a lift to the train station to continue his journey.
"He was not in police custody. Following the incident, whereby the man was injured, West Midlands Police have voluntarily raised the matter with the IPCC.
"We have been informed by British Transport Police that the man remains in a critical condition in hospital."
Chief Insp Southern said officers "were alerted to the fact the man may need a lift" and helped him with his journey. She said the man was not involved in anything suspicious at the time.
"There is nothing to suggest anything untoward, it was a simple encounter," she added.
She said the force had referred the matter to the IPCC at the earliest opportunity. Usually forces are only required to do so if someone has died shortly after being in contact with officers.
The incident, which is also being investigated by British Transport Police, shocked rush-hour commuters yesterday morning, and caused havoc on the transport network.
Colin Green, of Hands-worth, was taking his young son Lance to school when they saw the man throw himself under the tram at about 8am.
He said: "My nine-year-old boy was ten feet away when it happened. The man had been dropped off at the station by police.
"When the police drove off he walked past us and just jumped in front of the tram.
"The tram driver blew his horn when he saw the man close to the platform and when he jumped he put his brakes on.
"My son saw it happen, I tried to cover his eyes," he added.
The accident caused havoc across the network, which was shut down for several hours from Black Lake at West Bromwich to Birmingham Snow Hill.
Commuters heading into work in Birmingham city centre found themselves late arriving and four hours after the early morning accident the major part of the Midland Metro route was still out of action as British Transport Police investigated.
Midland Metro spokesman Phil Bateman said the drama at the stop, on the border of Smethwick and Birmingham, had caused severe disruption for travellers heading in and out of Birmingham.
"The accident happened just before 8.15am and caused us to have to shut down the power supply to the Metro system.
"All services between Black Lake in West Bromwich and the Birmingham Snow Hill terminus, and the return journey to Black Lake, were suspended and were still out of action four hours later."