The 29-year-old was unable to come to an agreement with Atletico regarding a new contract and left on a free transfer when his deal expired at the end of June.
Hermoso was linked with a number of clubs, including Manchester United, before it was confirmed that Roma had agreed to sign him on a three-year contract.
The Spaniard has made nine appearances for Roma this season, including six outings in Serie A, but he has missed their last three matches in Italy's top flight due to a mixture of suspension and injury.
Hermoso has admitted that it has been "very difficult" in Italy this term, with Roma struggling down in 12th spot in the Serie A table, while there have already been three managers at the club during the 2024-25 campaign.
Hermoso opens the door to Real Madrid move
Real Madrid are believed to be considering a mid-season move for Hermoso, with Los Blancos searching for a new centre-back, having lost Eder Militao for the remainder of the season due to a serious knee injury.
Hermoso has said that "it is an honour" to be linked with the Spanish and European champions, and he has refused to rule out a return to Spain in the near future.
The defender was a part of Real Madrid's youth system between 2005 and 2014, and he went on to represent Real Madrid C and Real Madrid B before making the move to Espanyol in 2017.
"It's been very difficult. In the team, however, despite the changes of coaches, there is a great atmosphere, even if we are not yet finding continuity in the league," Hermoso told AS.
Hermoso talks-up potential return to La Liga amid Roma 'difficulties'
"Personally, however, I have adapted quickly. And then there are the Argentines and Angelino, also Spanish, who help me out. Two coaches have already been dismissed. It's not easy, honestly. I wasn't used to these changes, but football is like that and you have to adapt. We will soon find consistency in the results, I hope, and we will be able to turn the situation around.
"Real Madrid's interest? I read about it. Many friends told me. It happened in various transfer sessions.
"Every time you are associated with big teams like Real Madrid it is an honour. I was in their youth team and I am grateful for everything they've done for my development.
"A return to Spain? I am 29 years old, most of my career has been in Spain, I like La Liga football and being in your home country makes everything easier. That's why I can't close the door to my possible return to Spain."
Hermoso represented Atletico between 2019 and 2024, making 174 appearances for the Red and Whites in all competitions, helping Diego Simeone's side to win the 2020-21 La Liga title in the process.