SaiRat have the same blood group (AB negative) and very recently Chavan saab donated his blood to save his badbad devi.
Sai can donate blood to Virat (he's a police officer and has to handle goons etc. so there's a greater risk of being hit by a bullet when in action) and Virat to Sai in emergencies (if chavan khandan's successor needs to be delivered via cesarean section) no need to look for a suitable donor because they both are AB negative and it is the rarest of the eight main blood types.