Watford have completed the signing of Birmingham defender Mathew Sadler on a three-and-a-half-year deal for an initial fee of £750,000.The Hornets have been short of defensive cover following Danny Shittu's trip to the African Nations Cup with Nigeria and Calum Davenport's premature return to West Ham after breaking a bone in his neck during last Saturday's 1-1 draw with Charlton.

The 22-year-old left-back was a regular for former manager Steve Bruce as Birmingham won promotion to the Premier League last season but has lost his place to Franck Queudrue and has seen new boss Alex McLeish bring in David Murphy from Hibernian this month.

Sadler could cost Adrian Boothroyd's side up to £900,000 depending on appearances and Birmingham have also installed a sell-on clause.

He has not played in the FA Cup this season with Birmingham so could make his debut on Saturday when Watford host Wolves in the fourth round.

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