It was reported that Porta had signed a 5-year contract with Siena for approximately €3 million. On 16 March 2008 Porta debuted for Siena in a 4–0 loss to Reggina Calcio when he was substituted onto the field for Tomas Locatelli on 62 minutes. The match proved to be his only appearance in the 2007–2008 Serie A season.