Costa scored 20 times in Chelsea's 2016-17 Premier League title-winning campaign, but the 28-year-old is said to have had a strained relationship with head coach Antonio Conte in the second half of the season.
In June, Costa revealed that Conte had told him to leave Stamford Bridge this summer, and their relationship is said to be beyond repair following a leaked video of the centre-forward seemingly 'mocking' his manager.
Atletico are currently under a transfer embargo, meaning that they will not be free to sign any new players until January 2018, and Simeone remained coy when questioned on a potential move for the Brazilian-born forward.
"I don't want to comment too much. The fact is he is still with Chelsea. The most important thing to me is the work of my club in general, not only in training. I have to work with what I have," Simeone told reporters after Atletico's 3-2 win over Brighton & Hove Albion on Sunday afternoon.
Costa fired Atletico to the 2013-14 La Liga title with 27 goals in 35 league matches, before leaving for Chelsea.