The Germany international has missed the Foals' past two games with a broken toe, but with the aid of a special supportive boot, he can make his return against Mainz.
"Marco is feeling good and he was able to train with the team yesterday and today," reported Favre at the pre-match press conference.
"He is ready, even for the starting XI. With the exception of Joshua King, who still has a groin problem I have everybody on board."
Without Reus, Gladbach have picked up just a point in two games to fall down to fourth in the table, seven points adrift of the league leaders Bayern Munich.
A win on Sunday would see them reduce that gap to four points and give Gladbach at least a top-four finish to 2011, which is in stark contrast to where they were only 12 months ago.
Favre has already tripled the tally of 10 points the club had at the winter break last season, but he now wants more by extending his side's unbeaten record at the Borussia Park this season.
"We have been very stable at home and played very well here," he said.
"The self-confidence that we have built up and the support from our fans certainly help us."
While Borussia's home form is admirable, there is only one blotch on Mainz's away record this season.
Their defeat in Kaiserslautern is their only loss on the road, where they have won one and drawn a further five.
"It is a sign of quality when you can be so consistent away from home," said coach Thomas Tuchel.
Tuchel can welcome captain Nikolce Noveski back into his squad for Sunday's game, although the Macedonian is not a candidate for a place in the starting XI.