Answer: Face to face communication
Step-by-step explanation: In simple words, constructive criticism refers to the process of giving opinion about others but in a positive manner and not insult others. Such opinions can be positive or negative.
In the given case, face to face communication is best choice as the manager wants to give negative opinions. In face to face manager can convey the message in a manner it is intend too and can also observe teh behavior of the receiver.