The preseason match finished 1-1, with Charly Alcaraz sent off for Southampton and Alessio Romagnoli for Lazio.
Gila later told Lazio's website: "I'm very happy to be back, I missed the pitch a lot. I think we're finding ourselves a bit.
"I love and the feeling of belonging in the group, the images of the fight are not beautiful but they show that we fight for each other. Today we played a difficult match against a good team and, as the coach said, we missed a bit in finishing."
The Spanish centre-back continued: "I have a lot of faith in the team, I see a lot of potential. Team objectives? I want much more than what we did last season. In the end I think that the potential to go to the Champions League places that we all dream of is there. Due to my characteristics I feel good when I go to the man, I'm happy because the team is very committed to what the coach asks for."