The defender is on the verge of joining the Russian club after Roma accepted an offer of £30.7m for him.
The Greece international was due to have his medical on Wednesday, but he has reportedly not shown up after a dispute over personal terms.
And now, according to Premium Sport, Chelsea have swooped to try and hijack Manolas' move to Zenit.
The Blues have been tracking the centre-back for months and they may now finally be making their move at the 11th hour.
Roma, however, will reportedly not sanction a sale to Chelsea unless they match Zenit's offer in full.