The South Korean forward returned from international duty earlier this month with a minor calf injury and missed the 3-0 defeat to Crystal Palace last weekend, with Nuno Espirito Santo stating before the match that the 29-year-old is "not so well".
Sessegnon was another who returned from the international break with a knock, while Dier was forced off before half time in the loss to Palace with a dead leg.
Although Nuno would have liked a fully fit squad to choose from for their opening Group G match, the Portuguese boss is now hoping that all three players can be available for selection on Sunday for their Premier League clash at home against London rivals Chelsea.
Both players started in the first leg of their Europa Conference League playoff tie against Pacos de Ferreira last month and have been training with the senior side in the build up to Thursday's game. body check tags ::