But Celtic manager Martin O’Neill was attracted to his “experience of high-level football”.
“He has also been involved in European competition, so we are bringing in a talented, experienced, international forward to really enhance our attacking options,” he told Celtic’s website.
Adamu becomes Celtic’s third signing of the January transfer window – all loans.
Czech Republic striker Tomas Cvancara has already found the net after arriving from Borussia Mönchengladbach, while Bournemouth full-back Julian Araujo has also made an early impression.
Adamu is eyeing a league and Scottish Cup double while scoring “a lot of goals” and wants “to improve as a player”.
“I’ve spoken with the manager and he’s given me good motivation and I trust him,” he said.
“He’s given me that trust, he’s told me how the system is and I feel the connection is really strong.”
Asked what kind of player Celtic fans will see in action, Adamu added: “I’m dangerous in the box and hungry for goals. That’s what the manager sees in me and I want to show that on the pitch.”