Seoul boss Choi Yong-Soo believes that the return of Adilson can help power his side into the semi-final of the AFC Champions League.
Seoul made the ideal start to the first leg against Al Ahli, going ahead after 10 minutes through forward Dejan Damjanovic.
However, Sultan Al Sawadi's equaliser ensured that the tie remains very much in the balance ahead of Wednesday's second leg.
With the Brazilian defender having served the suspension that kept him out of the tie in Saudi Arabia, Choi is hopeful that the 37-year-old can swing the balance in his side's favour.
"Adilson is a reliable player who has played for the club for a long period of time," Choi told the Asian Football Confederation website. "He is the core of our team and his return will definitely help our side."
The South Korean champions go into the clash in fine form, having avoided defeat in their last seven league games, with Choi's men sitting in third place.
However, Choi knows that the likes of Mustafa Al Bassas and Bruno Cesar will pose a threat to Seoul's hopes of qualifying for their first Champions League semi-final.
"Al Ahli were a strong team as I expected," he continued. "They are a team with good individual skills and teamwork.
"Al Bassas is promising player and he will be the future of Saudi Arabian football, while Bruno Cesar is also a splendid player who can control the game with experience and great finishing.
"But even though Al Ahli have a lot of good players, I believe that FC Seoul have many talented players and that we are well organised."
Vitor Pereira's men are unbeaten in their last five matches in all competitions, but have been held in both their league games since drawing with Seoul in August.
However, Ahli remain in second place in their domestic standings as they seek to go a step further in this year's Champions League.
The Saudi Professional League outfit were beaten 3-0 by Ulsan Hyundai in the final last time out.