Nugent slipped a disc in his neck recently and was not expected to play any part in the televised east midlands derby against the Rams on Saturday evening.
However, the striker was on the bench and came on to score twice in Leicester's 4-1 Championship victory to take his tally for the campaign to 11 goals.
"We didn't expect him to be right," said Pearson. "He decided he wanted to try it out on Friday in training. It was very much a case of seeing if there was a reaction on the morning of the game before we made a decision.
"He said he felt okay to play some part. Although he came off the bench, he has made a very good contribution.
"He doesn't like being injured and, at times, we have to protect him. Having said that, it is great to have players who desperately want to play a part even though they have been injured."