D'Alessandro heads for Roma exit
The winger, who has featured for Roma just three times, spent last season on loan at Cesena, helping the club to promotion from Serie B.
D'Alessandro will now get a chance to test himself on a regular basis in Italy's top flight after moving to Atalanta.
Roma, who were runners-up to champions Juventus last season, also revealed on Friday that Marquinho has agreed a €1million season-long loan move to Al Ittihad.
The Brazilian has made 56 appearances for Roma, whom he represented on loan before signing a permanent deal in 2012.
However, he was shipped out to Verona last season and will now head to Saudi Arabia.