The Welshman was named in Zinedine Zidane's squad ahead of the fixture, having overcome calf and hamstring issues.
The Wales international also sustained a thigh issue but made his return in the previous round of the Copa del Rey against Fuenlabrada at the end of November, providing a glorious assist moments after his introduction.
Another calf problem then consigned Bale to longer on the sidelines, although he featured in Madrid's Club World Cup triumph in December, and he gets the chance to prove his fitness in Cristiano Ronaldo's absence.
Bale is one of the few senior stars on show for Zidane's side at Numancia, with young talent including Theo Hernandez, Jesus Vallejo and Borja Mayoral included in the starting line-up.
Ronaldo, along with Toni Kroos, Luka Modric, Marcelo and Sergio Ramos, has been excluded from the squad to face the second-tier team in the first leg of the round of 16 at Nuevo Estadio Los Pajaritos this evening.
Karim Benzema also misses the tie, having suffered a hamstring injury during Real's 3-0 Clasico defeat at home to Barcelona in their last outing.
Zidane is marking the second anniversary of his appointment as Madrid's head coach, with the Frenchman under pressure because of the 14-point defecit between themselves in fourth and rivals Barca in first.
Real Madrid XI: Casilla, Carvajal, Nacho, Vallejo, Theo, Ceballos, Llorente, Bale, Vazquez, Asensio and Mayoral
Real Madrid subs: Navas, Varane, Casemiro, Acraf, Isco, Kovacic, Tejero
Numanica XI: Munir; Carlos, Medina, Dani Calvo, Ripa; Dani Nieto, Sierra, Pere Milla, Diamanka; Larrea, Higinio.
Numancia subs: Perez, Manu del Moral, Nacho, Fernandez, Valcarce, Etxeberria, Mateu