This was the fourth consecutive defeat between Serie A and Champions League, conceding eight goals in the last two.
"The players gave all they had today, trying to get back a game that started in the worst possible way," said Seedorf.
"It was a strange game and obviously the red card after five minutes changed everything. The lads did well to fight back to 2-2, but their determination to get the victory ended up leaving the team unbalanced and we suffered this defeat.
"We never gave up. At half-time I told the players to believe, as even with 10 men we've seen before that teams can improve and get important results. They did well to get back on the field with that reaction and on 2-2 we perhaps should've read the situation better to avoid the counter-attack."