The Leicester midfielder was shown a yellow card for a heavy challenge on Cole Palmer in the first-half of the Premier League clash.
Replays showed he caught the Blues star on his Achilles with his studs.
The incident was checked by VAR, who saw no issue with the on-field decision and did not order a review.
It is understood VAR deemed that Ndidi came from a short distance and the challenge lacked intensity.
Former England star Bent disagreed, though, and fumed at the lack of action on commentary for talkSPORT.
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He said: "It's awful. There's intent there. The ball is nowhere to be seen.
"I'm a little bit surprised they're not going over to check it. Is it endangering an opponent? Yes.
"The fact the referee isn't checking is a bit naughty. He's got away with one."
Bent continued: "It's blatant. He's extremely lucky. It's dangerous - and the fact they haven't checked it is bizarre."
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Ndidi was one of three Foxes players cautioned by Andy Madley during the first 45 minutes.
Boubakary Soumare and Oliver Skipp were both shown yellow cards for fouls of their own.
Meanwhile, Moises Caicedo also went into the book for the visitors in a physical opening half.
It was eventful for VAR as well after the Blues were denied a second goal by the officials.
Noni Madueke had found the back of the net before a check spotted Marc Cucurella was offside during the build-up.
Nicolas Jackson's 15th minute strike remained the difference between the two sides at the break.