Both centre-backs missed Dortmund's narrow 1-0 Bundesliga victory over Augsburg on Friday, Schlotterbeck due to illness and Sule with a swollen toe. However, coach Niko Kovac is likely to have the pair back in contention for Wednesday's trip to the Etihad Stadium.
According to reports, Schlotterbeck is training individually but is set to rejoin full training on Tuesday, with Kovac hopeful he will be fit to start. Sule, meanwhile, has recovered well and is also expected to make the travelling squad.
Kovac has been eager to have his defensive regulars available for what will be one of Dortmund's toughest tests of the campaign. The return of Schlotterbeck and Sule will be particularly significant as Dortmund attempt to contain former striker Erling Haaland, who has already scored 18 goals in all competitions this season for City.
Dortmund currently sit one place above City in the Champions League league-phase standings with seven points apiece from three matches, and know that a positive result in Manchester could be decisive in their push for direct qualification to the knockout stages.
Kovac has said in recent weeks that his side must show "responsibility and discipline" against Europe's elite sides, and having his first-choice defenders back gives him a timely lift.
The German side will train in Dortmund on Tuesday morning before flying to England, with final fitness checks planned ahead of the high-profile fixture at the Etihad Stadium.
Mikel Arteta has admitted Arsenal must remain grounded despite their stunning start to the season, as the Gunners continue to battle on multiple fronts at home and in Europe.
Tottenham manager Thomas Frank has eased fears over injuries to Mohammed Kudus and Djed Spence ahead of Tuesday's crucial Champions League clash with Copenhagen.
Real Madrid have been dealt a major setback ahead of their Champions League trip to Liverpool, with teenager Franco Mastantuono ruled out through injury.
Bayern Munich defender Hiroki Ito has returned to full training following a metatarsal fracture sustained earlier in the season.
