On 6 August, while away on international duty, Mattock was ecstatic when informed by his agent that West Bromwich Albion were interested in him. Eager to leave Leicester, he submitted his transfer request to chairman Milan Mandarić. The manner in which Mattock made the request infuriated manager Nigel Pearson. He signed a three-year contract with West Brom four days later for a fee of £1 million, citing Richard Stearman as his motivation for leaving Leicester. The comment angered many Leicester fans and he was booed upon his return to the Walkers Stadium in November.