The France international forward has been sidelined with a hamstring injury since early in December
France international Dembele has had a string of injury problems, with a hamstring complaint sidelining him since the game with Cadiz on December 5.
He returned to training on Sunday, but the Liga game with Valladolid on Tuesday will come too soon for the forward.
“He did part of the training session with the reserves yesterday, which is normal the day after the game,” Koeman said at a press conference on Monday. “He needs more training sessions to be able to go on the squad list.
“He could make the squad for Eibar at the end of December.”
Koeman’s focus is on reviving Barcelona’s fortunes, and said they cannot afford any more slip ups if they are to get in the title hunt, and he has said there has been no talk about the January transfer window.
“I’m talking to Ramon Planes about sport-related issues, not with anyone else,” Koeman said. “I don’t really want to because I think we have to wait for a new president.
“Right now I have to manage the team, prepare for our matches, there are lots of games. There isn’t even much time to talk about other things. We’ll see what happens in January.”
While Barca are eight points off Liga leaders Atletico Madrid, having lost four games already, Koeman feels the club are tracking in the right direction.
“Today it’s a team where we need to change a lot of things,” he said. “Younger players are playing and that’s why we have been a little inconsistent. We are also missing some players.
“For the future it looks good, but at Barcelona you have to win and battle for titles and it’s a complicated situation.”
French defender Clement Lenglet was surprisingly benched in the 2-2 draw with Valencia on Saturday, and Koeman insists it was purely on account of workload.
“I think it’s just part of the shuffling of the lineup we have to do for physical reasons,” the Dutch coach said. “It’s impossible to keep up the pace in such a short amount of time.”