Cardiff were promoted to the Premier League after winning the Championship title by eight points last season, but Hartson has admitted that previous top-flight experience could prove key to the Bluebirds avoiding relegation next year.
The 38-year-old told BBC Sport: "He will be massive for Malky Mackay next season. Craig's got great experience of the Premier League. He's got real quality.
"I'm working now with Craig with the national team and he's a great influence around the place."
The former Liverpool attacker played 33 times for Cardiff last season.