David McGoldrick's late winner settled a gritty and hard-fought contest at Portman Road, but Pearson was left fuming by a flashpoint just before the goal that rattled Foxes skipper Wes Morgan.
The City manager accused Michael Chopra of kicking out at him and then Daryl Murphy elbowing him.
Seconds later he was robbed by the latter, whose slide-rule pass put McGoldrick clear and he produced a cool finish past goalkeeper Kasper Schmeichel.
"We weren't at our best but still had enough chances to get something out of the game, although other off-the-ball incidents contributed to the result," said Pearson.
"All you have to do is take a look at them. I'm not a sour grapes person.
"Mick (McCarthy) is doing a really good job here and I don't want it to turn into me looking for excuses, but unfortunately a couple of very unsavoury incidents possibly contributed to what happened.
"He (Morgan) got booked for complaining about somebody elbowing him in the face. Everyone could see that.
"Chopra kicked him off the ball just prior to that."