The move comes after back-up goalkeeper Rafael Cabral suffered a season-ending knee injury against Swansea City last Thursday.
And with concerns over the fitness of first-choice shot-stopper Pepe Reina, the Serie A club have opted to add squad depth by securing Doblas' services until the end of the campaign.
A statement on Napoli's website confirmed: "Toni Doblas has signed a contract that keeps him at Napoli until 30 June 2014 after passing a medical."
Doblas, 33, has previously enjoyed spells with Real Betis and Real Zaragoza.
The Spaniard links up with Rafael Benitez's side after having his contract with Azerbaijani side Khazar Lankaran terminated in July last year.
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