As a defendant you should have filed a criminal complaint against the plaintiff, if the plaintiff has created a false document.
Since you have not filed a criminal complaint, the inference of the court would be against you holding that your statement is a mere allegation without substance or proof and it may form a good ground for the plaintiff to succeed.
It is necessary to file a criminal complaint against the plaintiff for fabricating a false document.At the time of evidence the false fabricated document must be sent for forensic report , the court will send the document for forensic examination and report on the application of the concerned person.
Mr. Khaleel is right. The failure to file a criminal complaint will not in any manner prejudice your suit. You can file an application in the suit to refer the forged document for forensic examination and once the same is established, you can get the suit dismissed.