The west London side said that Thorgan, a 19-year-old forward, will join their under-21 squad "to continue his pre-season development and a loan move is being considered".
The teenager, a Belgium youth international, moved to the Ligue 2 club in northern France at the age of 14 and made his debut in the senior squad last season, going on to make 14 appearances in all.
His brother signed for Chelsea from Ligue 1 club Lille in June for £32 million ($49.6 million, 41 million euros).
"Should they both play for the Chelsea first team, the Hazards will join a list of previous Chelsea brothers -- Ray and Graham Wilkins, Ron and Allan Harris, John and Peter Sillett and Chris and William Ferguson," Chelsea said on its website.
Source: AFP
Source: AFP