If I understand it good, your controller has to look like:
public ActionResult Edit(int id) { Partner partner = db.Partners.Find(id); ViewBag.Sifra = new SelectList(db.Partners, "Sifra", "Naziv", partner.Sifra); return View(partner); }
view:
@Html.DropDownList("Sifra", null, new { disabled = "disabled"})