Keegan is said to be targeting Helveg after cooling his interest in Chelsea full-back Mario Melchiot due to his demands for personal terms.
Looking at Hristov you'd expect him to be a towering centre-half, or perhaps a targetman of the Jan Koller mould, but if you saw the gangling Bulgarian in action in Portugal then you'd know that, surprisingly, he's actually quite a skillful centre-midfielder. He's comfortable with the ball at his feet and scored eight goals from midfield last season.
The 30-year-old currently plays for German side Kaiserslautern, where league rivals Wolfsburg are said to lining up a €1.75 million bid, so with just a year on his contract an offer of around £1 million could be enough to tempt him to England.