The officer, who has not been named, is being probed after carrying out a so-called tactical contact to deliberately stop the 17-year-old riding dangerously in Erith, south-east London, in November last year.
-> Police 'absolutely right' to knock moped thieves off bikes says Theresa MayThe police watchdog, the Independent Office for Police Conduct (IOPC), confirmed it is also investigating a second tactical contact case involving another Metropolitan Police officer, which featured an adult moped rider in Ealing, west London, in March.
The second case is not a criminal investigation, but comes amid divided political opinion over use of the tactic.
The watchdog said it is due to submit a file of evidence to the Crown Prosecution Service (CPS) and to Scotland Yard imminently.
If the IOPC recommends a prosecution, it would then be up to CPS bosses to decide whether or not to press charges against the officer, which could include actual bodily harm and grievous bodily harm.
The Met would also make a decision on whether the matter amounted to a misconduct allegation, which could result in the officer leaving the force.
The IOPC launched its first investigation after a Met Police car collided with the 17-year-old in Eastern Way, Erith, at about 2.15am on November 7 2017.
The teenager, who was not wearing a helmet, was admitted to hospital with serious head injuries and fractures but was later discharged.
He later pleaded guilty to five offences at the youth court, including theft, dangerous driving, and driving without a licence.
An IOPC spokesman said: "Ultimately no police tactic can ever be used with impunity in a country where we police by consent - be that tactical contact, the use of firearms or the use of restraint.
"It is always a matter of whether it's reasonable and proportionate in the circumstances.
"If it is - for example, as we saw at Westminster and Borough Market - then our investigations treat the officers as witnesses throughout and their conduct is not in question.
"But it would be wrong to offer guarantees in every case. Independent scrutiny is a vital part of public confidence in the way policing is done."
Senior officers have defended the use of tactical contact, saying it was needed to stop dangerous chases and has helped reduce moped-enabled crime in London by more than a third.
The manoeuvre has also been backed by Prime Minister Theresa May, who said a "robust" response was needed from police to what she described as a growing problem of people using mopeds to commit crimes such as bag- and phone-snatching.
But Labour has raised concerns about the approach, which shadow home secretary Diane Abbott said was "potentially very dangerous".