FC Seoul coach Choi Yong-soo believes the winner of the match on Tuesday between his side and defending AFC Champions League champions Western Sydney Wanderers will qualify for the last 16.
After three matches, both sides are on four points with one win, one loss and one draw, after their goalless draw in Seoul last month.
"The game tomorrow is a very big, important game. I think the winner of the clash will be going through this group stage. Tomorrow's game will be the decider," said FC Seoul coach Choi during Monday's pre-match press conference.
"It's a really hard group, we call it the group of death, and it's a really important match tomorrow to pass, to ensure we can qualify.
"This is actually the fourth game against the Western Sydney Wanderers and for us this is an away game and players are not match fit which is a disadvantage, but we trust the players and we focus and we plan to win the game tomorrow.
"Finally last weekend we won one game and that changed the whole team atmosphere into positive things," added Choi.
"We will send all of our best players on the pitch tomorrow. The team atmosphere is really good since last weekend's match."
After winning last year's semi-final between the two sides in the Parramatta Stadium 2-0, Choi's Western Sydney counterpart Tony Popovic is in confident mood heading into the clash.
"It's an important game, that's for sure. We're at the half way mark and there are three games to go and there could be a lot more twists and turns," said Popovic.
"I don't think it's do or die tomorrow night, but you can take a step forward in your chances of going through.
"We know tomorrow night they possess players that could win a game at any moment, but they also respect us and they know we beat them in the semi-final last year and we took a point off them a few weeks ago.
"There will be a lot of respect amongst both sides, but in the end if we get the three points, that's all that matters."