Can he sue my dad

So my dad was working for this man for a year then quit in December and the job finder company who gave him the job is now saying his old boss is going to sue him but my dad didn’t do anything wrong it was the person who worked there before him who did the accounts wrong and my dad didn’t touch those accounts and also his boss was very dodgy everyone who would work for him quit and he even shaved off his hair to pass a DRUG TEST and my dad got a text from another branch of the same company to call them asap we don’t know if its becuse of his old boss suing him or becuse he applied for more jobs there and my dad said hes not going to call them back

Any help please