Leicester forward Jamie Vardy is nursing an ongoing groin problem and could miss Wednesday's match.
Jamie Vardy's penalty and Maddison's magnificent volley, which capped a trademark Leicester counter-attack, had the hosts 2-0 up inside 23 minutes on Saturday, and there were no further goals in the match.
His exquisite first tough brought the ball down and he juggled past Adrian Mariappa - who got a touch - before volleying into the bottom corner from 18 yards.
Watford struggled as an attacking force - failing to register a single shot on target - and Demarai Gray hit the post for Leicester in the closest either side came to a goal after the break, the day getting worse for the visitors when Etienne Capoue was sent off in the last minute. It was a really good counter attack, a good team goal.
"I needed to make an impact to make amends and thankfully I did that and hopefully that is in the past now".
"I'm sorry. In this moment, my mind is only on my team and how I can help my players improve and play together to be a strong squad". I'm really chuffed with that one.
"I don't know (if he will need surgery)".
Leicester City's penalty shootout win over Southampton, after the game ended scoreless in normal time, in the EFL Cup during the week was followed up with a win against Javi Gracia's Watford.
Their misery was underlined when Capoue was shown a straight red card when he went in two-footed on Iheanacho a minute from the end.
Vote in the Irish Independent Sport Star Awards and you could win the ultimate sports prize. I spoke to Iheanacho and he said there was no contact by Capoue.
"But if I am interested I won't tell you", Ranieri said on the signing of Danny Drinkwater. It doesn't depend on me but we are going to appeal.
"If I say my opinion it will sound like an excuse".
Some fans had stated that they felt he had been a "revelation" for them this season, whilst others felt he had been one of their standouts in the game against Watford. I prefer to keep my opinion to myself.
"People have been questioning why we are taking 2 banners to Leicester tomorrow that are not #Watford related".