 Despite finding his form at Messina, Donati still found himself out of favour at Milan and was again sent on loan, this time returning to his first club Atalanta for the 2006–07 season.Donati was a youth international, representing Italy at under-16, under-18, under-20 and under-21 levels.On 29 June 2007, Celtic confirmed the signing of Donati on a four-year contract for a fee of €2 million.