Pearson was taken to hospital after the Championship leaders' 1-1 draw with Blackburn Rovers on Saturday, and remained there to undergo further tests.
The result at Ewood Park extended Leciester's unbeaten run to 17 games, but that achievement was overshadowed by Pearson's ill health.
Leicester revealed the 50-year-old had been suffering from sickness prior to the match and took the decision to be checked over.
A statement on the club's official website on Monday read: "After the match, Nigel took the decision to seek medical advice and to attend hospital for tests, as a precautionary measure.
"He remains in hospital at this stage and will undergo final tests on Monday morning.
"The club would like to reassure supporters that Nigel is very well and in great spirits."
Pearson has been in charge at Leciester since November 2011 and the club appear certain to gain promotion to the Premier League this season, with third-placed Derby County currently 15 points behind having played a game more.
