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 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.”
The 20-year-old Arthur has made just three appearances for Premier League outfit Brentford, including two starts in his season’s League Cup.
However, O’Neill thinks the England youth international is “an excellent player, with real attributes, good height, strength and speed”.
All four of Celtic’s January signings have been loans, the others being Czech Republic striker Tomas Cvancara from Borussia Mönchengladbach and Bournemouth full-back Julian Araujo.
Meanwhile, Kenny heads for the side sitting third in League One having failed to become a first pick since O’Neill’s return to Celtic.
The 22-year-old Irishman, signed in January 2024 from Shamrock Rovers, has played 22 times for Celtic this season, 12 of them starts, and scoring six times.