Does it look soft like filled with fluid or hard looking.
Looks soft to me in the pic.
Once they have lumps like this filled with puss best issolate incase it burst as it can infect the whole tank.
Gourami are very prone to bacterial infections. http/www.badmanstropicalfish.com/articles/article25.html
Like it said in that article lumps that just appear are usually bacterial.
Not sure what meds are available in your country ask the lfs they will point you in the right direction.
Fingers crossed for him and good luck.