The 22-year-old left Gelsenkirchen for Gladbach before the start of the season for a knock-down price of 10 million euros ($11m). Schalke had paid FC Basel 26.5 million in 2016 for the Cameroon-born forward.
After an injury-hit spell with the Royal Blues, including a horrific ankle injury just after joining, Embolo has rebooted his career at Gladbach, helping them spend 10 weeks at the top of the Bundesliga before RB Leipzig finished 2019 in first spot.
A win for Gladbach in Gelsenkirchen would put them back in first place at the start of the first weekend following the league's four-week break.
Embolo has scored six goals in 14 games in a potent attack alongside fleet-footed winger Patrick Herrmann and French strikers Alassane Plea and Marcus Thuram. The quartet have contributed 22 of Gladbach's 33 goals.
Gladbach sports director Max Eberl told German daily Bild that Embolo took a salary cut to join.
"He was willing to give up money for us and has shown that he has got back into the rhythm," Eberl said.
Head coach Marco Rose describes Embolo as a "really good bloke. It's great when this colossus smiles at you, he's a team player, who has big goals".
Gladbach's fans are dreaming of a first league title since 1977, but Rose insists on keeping expectations down.
"We have achieved an outstanding position in the first half of the season, we want to build on that," he said.
Gladbach will be without injured defender Ramy Bensebaini, who scored both their goals in last month's 2-1 home win over defending champions Bayern Munich.
Schalke have strengthened their defence by signing France Under-20 talent Jean-Clair Todibo on loan from Barcelona for the rest of the season with a buy option of 25 million euros.
Schalke head coach David Wagner called Todibo "one of the best young centre-backs in Europe at the moment".
Schalke will be without goalkeeper Alexander Nuebel, who is serving a four-match suspension after being sent off for a karate-style kick in their 1-0 win over Frankfurt before Christmas.
Nuebel has also been stripped of the Schalke captaincy after it was announced a fortnight ago that he will join Bayern Munich at the end of the season.