Schalke coach Thomas Reis says he doesn't know when Liverpool loanee Sepp van den Berg will return from the sidelines.

The Dutch defender has been out of action since October when he suffered an ankle injury during the 3-2 defeat to Augsburg. As a result, he went under the knife to repair the damage to his left foot.

"With Sepp, it's the case that he won't be available to us for a while. I can't predict how long that will be," he said.

"He still has the same problem with the operated foot. It's hard to predict when he'll be able to complete the training without pain."