Osimhen needed to leave Napoli after the club he led to the 2023 title signed Romelu Lukaku, but was unable to agree a deal with potential suitors Paris Saint-Germain and Chelsea before the European transfer window closed.
He has thus joined Turkish club Galatasaray on loan for the season - though a January transfer window break clause is reported to be included, while also extending his Napoli contract for one more year, through 2026-27.
"I'm excited to be here and I can't wait to see you at the stadium. Let's go," Osimhen said on Instagram while wearing a Galatasaray shirt inside his new ground.
At 25, the Nigeria forward still has a lot of years to play top-level soccer. Known for his aerial prowess and face mask, he has scored a total of 76 goals in 133 matches across all competitions for Napoli since joining four years ago.
Also announced in Wednesday was a move for former Borussia Dortmund defender Hummels to Roma.
"Hi Giallorosso fans, this is Mats, a new player," Hummels said in a video published by Roma. "I'm really happy to play for this club in front of you and see you in the stadium."
Hummels, who is a free agent, has not previously played outside Germany.