"Liverpool are tough. They have a few fantastic players like Steven Gerrard," said Koeman.
"If you beat Barcelona 2-1 on their own turf you are a very strong team. It will be a hell of a job so it will be important to get a good result in our own stadium.
"It is a real disappointment. I do think that all clubs are tricky, but the fact is that we already had them in the group stage.
"You want to go somewhere else - all other clubs would have been nice."