The Blues have been busy strengthening all areas of their squad this summer, including in central defence with the addition of Axel Disasi earlier this month.
While Chelsea boss Mauricio Pochettino can now call upon Disasi, Benoit Badiashile, Levi Colwill and Thiago Silva, his defensive options were weakened by the news that Wesley Fofana is likely to miss the majority of the season with a knee injury.
As a result, the West London club are seemingly open to the prospect of reinforcing their defence and are scouring the market for possible additions.
According to Foot Mercato, Chelsea have identified Relvas as a potential transfer target, and they have made an enquiry for the Portuguese defender.
Relvas, who has been scouted by some of Europe's biggest clubs, has spent the last three years with Portimonense.
After initially linking up with the club's Under-23 side, he stepped up to the first time ahead of the 2021-22 season.
Since making his debut in August 2021, the 23-year-old has gone on to make 69 appearances for the club across all competitions.
The versatile defender predominantly plays as a centre-back, but is also capable of playing on the left side of defence.
Relvas is under contract with Portimonense until June 2026, and he would reportedly be a relatively cheap option at less than €10m (£8.6m).
Should Chelsea decide to pursue a move for Relvas, they could face competition from several clubs across Europe, including Benfica, Besiktas and Wolfsburg.
Monaco are also showing an interest in signing Relvas, as they consider alternatives to Fulham centre-back Tosin Adarabioyo.
The Ligue 1 side have been in pole position to sign Adarabioyo for most of the summer, but there are now fears the deal could collapse.