Kallio becomes the second player of the day to sign for Sheffield United with the Blades also agreeing a loan deal for Sunderland defender Nyron Nosworthy.
toni kallio
The Finland international enjoyed a loan spell at Bramall Lane last November, but made just two appearances before being recalled due to a shortage at Craven Cottage.
He won't however be allowed to make his second debut at Vicarage Road tomorrow night due to the time he completed the deal - he could however feature against Derby County on Saturday.