Jesse Lingard looked to have given the Red Devils victory at Stamford Bridge before Diego Costa struck a last-gasp leveller.
It was frustrating for the visitors but the Blues manager felt it was nothing more than his side deserved in west London.
“I am happy with the reaction of the team,” the Chelsea boss said.
“Manchester United did a good job in the first half and in the beginning of the second, they are not an easy team to beat. But we deserved a point.
“We dropped too far back after the first 20 minutes when they dominated us but later on we closed a little more.
“They made a beautiful goal - without good marking from our side - but after I think the team reacted very well.”
Zouma, who was carried off a stretcher after landing awkwardly having leapt up for a loose ball, will be sent for tests tomorrow to determine the extent of the problem.
Chelsea's 1-1 draw with Manchester United in pictures:
“Tomorrow we know more, but if you have this injury - and everyone has seen how bad it is - hyper-extension is always bad,” Hiddink added.
“I had this same problem once and it hurts. But let’s hope and see tomorrow what the MRIs will show.”
Man United chief Louis van Gaal is under increasing pressure at Old Trafford as reports continue to claim former Chelsea boss Jose Mourinho is being lined up to replace him.
The Red Devils manager appeared under extreme pressure after the 1-1 result and was involved in a couple of spiky exchanges with the media.
He felt his team had done enough to win the game but knows they can’t keep letting in late goals.
“I’m frustrated and my players are frustrated when you are playing like we played today and you are not making the gap smaller,” Van Gaal said.
“You can say it is misfortune but it’s not the first time it has happened to us. Newcastle also scored late against us.
“I’m happy with the performance. It was not a boring match. I hope also to get the support of the media this week.
“I have to say that we played a very good match until the last quarter of the game.
“It’s frustrating that they scored in extra time and with the way that they scored because Daley Blind was slipping.
“We had the chance to score more goals and we controlled the game. It’s not easy to play here because the level of individual players in Chelsea is very high.
“It’s not easy but it was better than last year, which was 1-0 then.”