Suarez was not included in the squad for the game and the first question Koeman had to field from Catalan TV network, TV3 was about the striker as the Uruguayan continues to train apart from the rest of the squad ahead of a possible transfer.
Internacional lead Group E, three points ahead of second-placed Gremio, who lost 2-0 at Universidad Catolica in Chilean capital Santiago.
"The game was in fact over after my team saw a straight red card. However, my team tried their best to avoid a worse defeat," Duisburg head coach Torsten Lieberknecht said.
When asked about Suarez, who was also left out of a friendly against Gimnastic Tarragona at the weekend, Koeman said he had "spoken to him about the future and whether or not he will stay."
The changes mean that the weekend will open with Villarreal at home to Eibar, with Villarreal looking to improve on an opening day's performance that saw them held 1-1 at home by newly promoted Huesca.
"We are waiting for what the Ministry of Health and the president are going to say about sporting activity and give us direction and that is what we are going to do as to when football activity is starting and when there is a continuation of the league," he added.
"Our players are highly motivated to beat their opponents on Sunday. We are Esteghlal and can benefit from our previous experience in the competition," he added.
Former Birmingham midfielder Jude Bellingham is said to be a decisive factor as the 17-year-old impressed with his maturity when operating as a box-to-box midfielder.
Walter, who replaced Christian Alves in the 83rd minute, latched onto Jonathan Cicero's cross and needed just one touch before rifling a shot into the bottom right corner.
MADRID, Sept. 16 (Xinhua) -- FC Barcelona coach Ronald Koeman has admitted he is pessimistic about the club's chances of strengthening its squad before starting the new season.
Elsewhere, Villarreal came back from a goal down to take their first win of the season with a 2-1 victory at home to Eibar.