But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor [Comforter] will not come to you; but if I go, I will send him to you. [John 16:7 NIV, also see John 14:6]
A slight change in the Greek word Paraclete of the original text (“comforter”, or Holy Ghost”) turns the word into Paracleitos (“praised one”) which is the meaning in Arabic of the name Muhammad and its cognate Ahmad, also used of the Prophet. The Gospel would then echo the words of the Koran (61:6) 
And (remember) when 'Īsā (Jesus), son of Maryam (Mary), said: "O Children of Israel! I am the Messenger of Allâh unto you confirming the Taurât [(Torah) which came] before me, and giving glad tidings of a Messenger to come after me, whose name shall be Ahmed. But when he (Ahmed i.e. Muhammad SAW) came to them with clear proofs, they said: "This is plain magic." [Dr Mohsin translation of Quran 61:6]
Gospel of John
Christians tacitly admit the author of John was a liar and Bible scholars trust the author of John the least out of the four Gospel writers, thus such an unholy alteration would certainly be considered within the scope of the author of John. However, more worryingly, dishonest and shadowy figures exist in transmitting the Gospel of John (and the other three Gospels) after the demise of the original author as these shadowy figures (the scribes) are responsible for a known New Testament scribal forgery in the form of a huge CHUNK of text which even Christian scholars acknowledge as a forgery – John 7:53-8:11.
As the author of John is tacitly known as a liar within evangelical circles and those who transmitted the Gospel of John are grossly untrustworthy/deceptive we can have no qualms in believing some shadowy figure involved with the Gospels changed/omitted/or missed parts mentioning Prophet Muhammad (p).
 The Concise Encyclopaedia of Islam, Revised Edition, Cyril Glasse, Stacey International, 2001, p86
Tough questions for Christians