The 26-year-old Germany international, plagued by injuries in recent years, scored one goal and set up another in a 3-1 victory at VfB Stuttgart in the German cup quarterfinals on Tuesday, having returned days earlier from a virus infection.
Coach Thomas Tuchel said Reus was almost back to his best.
"He's a sensitive, creative player who needs to know that he doesn't have to think about his body. We're not there yet, but on a great path to getting there," Tuchel said.
"It's important not to ask for too much too soon, because we want to see him finish the season. But it's amazing how focused he is and how cleverly he's positioning himself."
Reus's nine league goals have helped Dortmund to 45 points, a haul that would normally have put them top of the Bundesliga at this stage were it not for Bayern Munich's near-flawless campaign, which has put them eight points clear.
The Ruhr valley club do, however, boast the best attack in the division and have scored 30 goals in their nine home games so far. Gabon international Pierre-Emerick Aubameyang, currently the Bundesliga's top scorer with 20 goals, has outscored the entire Hanover team, who prop up the division.
"It is good that we played on Tuesday (in the Cup) as we have a bit more time to recover," said Tuchel. "We have to be professional about our recovery now and then we will be 100 percent on Saturday."
Bayern, still on track for a treble after also reaching the last four of the German Cup last four on Wednesday, travel to Augsburg on Sunday in a Bavarian derby.
Third-placed Hertha Berlin, 10 points behind Dortmund, take on VfB Stuttgart, with striker Salomon Kalou doubtful following an injury in their Cup win on Wednesday.