The two then allegedly started assaulting the actor while pouring bleach on him.
A noose was said to have been tied around his neck during the attack.
Sources close to the singer told TMZ that both of the men were white and yelled that "this is MAGA country".
The actor was taken to a nearby hospital where it was reported he suffered a fractured rib.
Smollett has reportedly been the target of other attacks; US website ThatGrapeJuice also published abusive letters that the actor had recently received, saying, "You will die black f**".
Chicago police released a statement saying they were treating the attack as a "possible hate crime".
Police described the attack as a "racially charged assault and battery", describing how the offenders "poured a chemical substance on the victim" and "wrapped a rope" around the actor's neck.
Singer Zendaya and actors Jesse Tyler Ferguson and Kerry Washington were among the celebrities who took to Twitter to offer the actor support.
The actor announced he was gay in 2015 during an interview with Ellen DeGeneres, during which he said he hoped his coming out would help other gay people feel less alone.
Smollett has starred as Jamal Lyon, who is also gay, on the hit series of Empire for the past five seasons.
The showfollows the powerhouse Lyon family who dominate the music industry. Taraji P Henson and Terrance Howard also star.
