Gregg McKissock, 30, dropped George Thomson, 24, into the water in January this year.
Mr Thomson suffered severe hypothermia after being pulled from the river.
McKissock was jailed at the High Court in Glasgow after being convicted of attempted murder last month.
It emerged that McKissock had numerous previous convictions for assault.
Judge Sean Murphy QC told McKissock: “This incident can only be considered to be a very dangerous matter.
“Mr Thomson could not swim and he was a vulnerable young man. The temperature and conditions were such that he could have died because of hypothermia.
“This was so reckless that a considerable custodial sentence is inevitable.”
McKissock and Mr Thomson had been in each other’s company that evening and a jury heard there had been “no animosity” between them leading up to the incident.
But Mr Thomson recalled being grabbed and “tossed into the Clyde”. He battled to stay afloat before being pulled from the freezing water and rushed to hospital.
A casualty doctor told the court how it took a number of hours to raise the victim’s body temperature and that his life had been in danger.
McKissock’s lawyer said the murder bid had been “out of character” for the former mechanic.
Geoff Forbes, defending, added: “He continues to deny the offence, but he hopes the victim suffered no adverse effect as a result of this incident.”