The 29-year-old frontman joined Saints only earlier this year as they fought to survive in the Premier League, but failed to make an impact.
Onuachu’s former club Genk tried to re-sign the forward from the Championship outfit this summer, but a move did not materialise.
Onuachu was not in new boss Russell Martin’s plans as he failed to appear in any league matches for Saints this season.
And now he has joined Turkish giants Trabzonspor on a season-long loan deal from Southampton.
The Trabzon-based outfit will pay a €1.5m loan fee to Southampton in two instalments, according to Turkish broadcaster A Spor.
It has been also suggested that the Southampton loanee will earn €1.7m in wages from the Turkish outfit.
Onuachu was a prolific goalscorer in Belgium for Genk and will want to get his career back on track in Turkey.
