Hazard scored his 11th goal of the season as Chelsea beat West Ham 2-1 at the London Stadium last night.
The Belgian has been rejuvenated this season after difficult 2015/16 campaign.
Chelsea player ratings against West Ham United
Mon, March 6, 2017
Express Sport rates how the Chelsea players performed during their Premier League win over West Ham United at the London Stadium
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And Arsenal great Campbell is in no doubt about Hazard's quality.
But the former defender feels Hazard can reach his full potential by playing for Real Madrid or Barcelona.
Chelsea's Eden Hazard celebrates scoring
He told Sky Sports: "Sometimes you have to go to Real Madrid or go to Barcelona to be truly world class.
"He's world class but sometimes you have to go to those clubs to almost say 'look I've played at the biggest clubs in the world'.
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Chelsea's Eden Hazard celebrates scoring their first goal with Victor Moses
"Chelsea's a massive club but sometimes people do think that.
"To really see your potential as a world-class star, players do go to Real Madrid and Barcelona to kind of put that cherry on top of the cake."