Seedorf's place at the helm of the Italian giants has come under scrutiny recently amid speculation that he may be replaced at the end of the season.
But De Jong threw his support behind the head coach after Milan boosted their hopes of a sixth-placed finish and a UEFA Europa League spot, thanks to the Dutch midfielder's 65th-minute goal at San Siro.
"This game was doubly important," he told Sky Sport Italia after the final whistle.
"Everyone saw in recent weeks how tough it was for our team, so it was fantastic to win and we must continue along this path for Europe.
"We have never given up, so we have to carry on and I believe we can get a place in the Europa League.
"This victory is for him (Seedorf), as people talked too much about his position this week, but he is very important for the squad."
