Karthikeyan tweeted: "Don't know where all these Indy stories are coming from - defintely not me! Focus on F1 with HRT for 2013 so anything else is a no-go!"
The Indycar series has featured drivers both towards the end of their F1 career as well as before it.
The most recent example is of Brazilian Rubens Barrichello, who made his Indycar debut in 2012 after racking up the highest number of Grand Prix starts in F1.
Two-time champion Emerson Fittipaldi also raced in Indycars and Britian's Nigel Mansell won the 1993 title after his championship winning F1 campaign in 1992.