General opposites:
* आलसी (aalaasi): Lazy
* निष्क्रिय (nishkriya): Inactive
* कामचोर (kaamchor): Shirker
* सुस्त (sust): Sluggish
More specific opposites:
* अप्रभावी (aprabhaavi): Ineffective
* अक्षम (akshama): Incompetent
* अयोग्य (ayogy): Unfit
* अनुपयुक्त (anupyukta): Unsuitable
It's important to consider the specific situation to determine the best opposite. For example, if you're talking about someone who is not hardworking because they are lazy, then "आलसी" would be a good choice. If you're talking about someone who is not hardworking because they are incompetent, then "अक्षम" might be more appropriate.