Striker Lewandowski and full-back Contento sat out Bayern's 3-0 Dream Game victory last week due to injury, but they trained under the watchful eye of coach Pep Guardiola at the Sabener Strasse on Sunday.
Temperatures soared as the German champions were put through their paces and stepped up their preparations for the new season in front of around 500 fans at their training ground.
Bayern will take on Bundesliga rivals Borussia Monchengladbach next Saturday after locking horns with Duisburg.