Speaking to Sport Mediaset via FCInterNews, Inzaghi admitted both players were on painkillers amid an injury crisis at the San Siro.
Second-half goals from Marko Arnautovic and Hakan Calhanoglu inspired Inter to a clear-cut win against Lazio.
As such, the Nerazzurri will trade tackles with fierce rival AC Milan for the fourth time this season.
Asked if he was proud of Inter’s performance at the San Siro, Inzaghi replied: “Absolutely. We played a fantastic match against a top-level opponent. In the first half, we struggled, but we never lost our composure.
“We risked falling behind, but we broke the deadlock with Arnautovic’s great goal. Then, in the second half, we had to change formation out of necessity.
“But I have an incredible group of players, and I’m proud to be their coach.”
Meanwhile, he explained the current fitness status of two first-team strugglers.
“I got a lot of important responses from the team. Several players weren’t at their best, but they still stepped up. Frattesi and Taremi had serious issues and played through painkillers, but they never hesitated.”