Hello Inderpal07,
Since you are a new member of this forum, it’s understandable that you may not know it.
Like N.K. Sundaram pointed out, unless you give all and complete facts right at the beginning, you can only expect half-baked suggestions that most likely will lead you or your friend to more trouble than a solution.
You mentioned, "They say that the client has made a complaint against him. But either the complaint came in the notice period or even if it came earlier, no action was initiated before the notice period."
You yourself aren't sure of this fact. If you really wanted to help your friend (or for whichever purpose you posted this issue in this forum), you could have checked out the details and then posted them. Also, 'complaint' can mean anything. To the one who is the 'target', it could mean atrocious, to the company it could mean 'well-deserved', and to others like the members of this forum, it could be quite something else unless the details of what the complaint was all about come to the fore.
Hope you get the point.
This also leads one to another issue that's also not very common: "Valuing others' time as you would your own".
Regards,
TS