The 28-year-old's move back to Spain fell through and Costa has remained in Brazil, accusing Chelsea of treating him "like a criminal", and has yet to return to training with the London side.
"Diego and I have been playing together for three years, we have won everything together except for the Champions League," Hazard told Spanish sports news outlet Marca.
"It's a pleasure to play with him, he's a top player and a top person.
"I would like to see him come back but I don't make the decisions. I hope he can find a solution so that we can see him back on the pitch soon."
Chelsea have won the league twice in the last three years but Belgium international Hazard, who returned from an ankle injury during the nation's recent World Cup qualifiers, is expecting a tougher campaign this time around.
"There is not just one team, in the Premier League there are at least six or seven who can win the title," Hazard added.
"Every week you have to be ready for the fight because every week, if you aren't ready, you could lose. We will see at the end of the season who is best."
After the international break, Chelsea travel to Leicester City in the league on Saturday.
(Reporting by Aditi Prakash in Bengaluru; Editing by Clare Fallon)
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