The 34-year-old is without a club following his release from Aston Villa at the end of last season and is thought to be on the radar of several sides.
But Planes insists the Periquitos are not targeting the powerful frontman who has also been linked with Liverpool, Stoke and Norwich.
The Espanyol chief told Catalan newspaper Sport: "I know about the rumours in the papers but we are not interested in Heskey or any other footballer.
"The squad is closed and the coach has not demanded any more players. Espanyol have a mix of experience and youth this season and that is sufficient to obtain our objectives."