Reus suffered an adductor muscle injury during the DFB-Pokal final, and coach Thomas Tuchel said a first-team return could be some time away.
Thomas Tuchel has confirmed that Borussia Dortmund forward Marco Reus has returned to training following his groin injury.
Cologne boss Peter Stoger has advised fans against putting bets on the club to win the Bundesliga title this season.
The Foals, on a four-match unbeaten run against the Bundesliga champions, go into the match on the back of a 2-0 Champions League win at Celtic.
Hertha Berlin coach Pal Dardai has said that his side will go into Saturday's meeting with FC Cologne as favourites.