Dier has endured a frustrating 2023-24, with the England international not being viewed as first choice by recently-appointed head coach Ange Postecoglou.
That will change for the foreseeable future as Dier is required to deputise in the middle of the backline for at least the next two fixtures courtesy of Romero's ban.
However, the 29-year-old has just over seven months remaining on his contract at the Tottenham Hotspur Stadium, opening up the possibility of a January exit.
Reports have previously indicated that Spurs would be open to cashing in on Dier, while the player is not in any particular rush to make a decision over his future.
According to O Jogo, Sporting have started to monitor the situation ahead of a potential reunion.
Between 2003 and 2012, Dier was part of the youth academy at the Portuguese giants before eventually making an impact in the first team.
A total of 31 appearances were made for Sporting, with his performances eventually earning him a £4m transfer to Spurs who he has represented ever since.
That said, the report adds that Sporting are only interested in signing Dier on a free transfer at the end of the season, rather than in the January window.
In a recent interview at a web summit, Dier hinted that he was open to representing Sporting in the future, calling it "his home" and revealing that he would like to live there at the end of his career. body check tags ::