Belgian forward Eden Hazard could be as good as Lionel Messi and Cristiano Ronaldo if he changes his attitude, according to former Chelsea midfielder Michael Ballack.
The attacker has been pivotal to Chelsea's unbeaten start to the season, scoring six league goals in his first seven games, but has often experienced dips in form throughout his stay in London.
Ballack wants to see more consistency and a better work ethic from the 27-year-old but questions whether Hazard has the drive to be considered amongst the best in the world.
"You have to ask him if he wants to compete on that level because he has the ability," Ballack told CNN Sport.
"Sometimes he seems a bit happy with what he has, with the environment at Chelsea. He's a great player, he shines a lot, he can switch on his engine when he wants."
'Modric is a really good example'
Ballack points to the example of Real Madrid midfielder Luka Modric, who was recently named the FIFA Best Player of the Year.
"To be at the top, it's much more than having one good season. That's what I think he has to understand," continued Ballack, referring to Hazard.
"[Luka] Modric is a really good example of what you can achieve with hard work. From being a top player to having an absolutely world-class season."
"That's what his target should be because he has the quality."
Chelsea host Hungarian side MOL Vidi FC on Thursday in their second Europa League group game of the season, before a trip to Southampton just three days later.
Boss Maurizio Sarri rested Hazard for their first Europa League fixture against PAOK and he may be tempted to do the same again.
However, Ballack believes tiredness shouldn't be an issue with a team like Chelsea competing for more than one trophy at a time.
"Every big club has to deal with it -- this is a normal thing. When you're a big player you need to adapt to that rhythm, there's no doubt."
"It's not just being focused on one or the other. If you're a good player, playing for a great club, you have to play two or three times a week with no problem."
Ballack made 98 appearances for Germany in a 17-year career, playing in both the German Bundesliga and English Premier League.
The 42-year-old believes two of his former clubs, Bayern Leverkusen and Chelsea, have a good chance of making the Europa League final this year.
"A good final would be between a German and an English club, because I played in both leagues," he told CNN Sport.
"I would love to see [Bayern] Leverkusen and Chelsea obviously. It's a dream final for me to watch. But I see [RB] Leipzig also as a club who can reach the final."
'Ozil has to focus on is football'
Arsenal are the only other English club left in the competition and Ballack believes a number of their stars will find it hard to play in Europe's second-string competition.
He believes World Cup winner Mesut Ozil is someone who could shine in this season's tournament, if only he had the motivation.
"It's also a player who played on the highest level with Germany but also the Champions League," Ballack told CNN.
"These kinds of players playing just Europa League? It's a question of how much they really want to perform there."
Ozil stepped away from international football after the distratious 2018 World Cup, citing racism as a reason for the decision.
Fellow countryman Ballack believes the door is still open for a return to the German squad in the future.
"He's still a really really good player, but he had his reasons to step back from the national team -- the reasons are well known."
"He has to focus on is football, and maybe in the future things will change."