Luciano Spalletti said tension and anxiety got the better of Inter as the Italian side crashed out of the Champions League following their draw with PSV.
Mauro Icardi's equaliser rescued a 1-1 draw at home to PSV on Tuesday but it was not enough for Inter, who finished third in Group B behind Barcelona and Tottenham.
Inter needed to better Tottenham's result against Barcelona to progress to the last 16, however, Spalletti's men slipped into the Europe League following Spurs' late point at Camp Nou.
Head coach Spalletti bemoaned what transpired at San Siro, telling Sky Sport Italia: "We were unable to keep our calm, despite the fact everything was still possible.