Smalling joined Roma on a season-long loan deal back in August, after falling down the squad pecking order at Old Trafford under Ole Gunnar Solskjaer.
The 30-year-old has since racked up 37 appearances for the Giallorossi, scoring three goals, while helping them to finish fifth in Serie A and advance into the latter stages of the Europa League.
Roma boss Paulo Fonseca publically admitted that he would like to retain Smalling's services beyond the end of the current season back in April, telling Portuguese publication A Bola: "He's a great professional and person, it's a pleasure to have him here with us."
The English centre-back's loan agreement ran until the end of the 2019-20 Serie A campaign, but he has not been granted the chance to extend his stay in Italy to take part in the club's remaining Europa League matches.
Smalling delivered a message to his followers on social media confirming the news, writing on Twitter: "I’m gutted that I can’t finish what we started this season.
I’m gutted that I can’t finish what we started this season. To experience the love shown to me in such a short time was extra special and it will not be forgotten. I want to thank and wish all the players and staff the best of luck against Sevilla. DAJE ROMA! 💛❤️ 🐺 pic.twitter.com/9vHfpWUNsz— Chris Smalling (@ChrisSmalling) August 4, 2020
"To experience the love shown to me in such a short time was extra special and it will not be forgotten.
"I want to thank and wish all the players and staff the best of luck against Sevilla. DAJE ROMA!"
The Giallorossi will still have the opportunity to try and sign Smalling permanently now that the summer transfer window is open, and they are also free to explore the possibility of another loan deal in 2020-21.
Inter loanee Alexis Sanchez is also due to return to Old Trafford, but the Serie A giants are currently in the process of persuading United to part ways with the Chilean.
The Nerazzurri are on a course to meet the Red Devils in the Europa League final, and they want to tie Sanchez down to a permanent deal so he can aid their cause over the next couple of weeks.