Contradiction with Malachi 4:5
Malachi 4:5 mentions Elijah being sent before the great day of the Lord, whereas Matthew 11:10 refers to John the Baptist being sent as a messenger, which differs from Elijah's role.
Malachi 4:5: Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD:
Contradiction with John 1:21
John 1:21 includes John the Baptist denying being Elijah, contrasting with the implicit comparison of John to a prophetic forerunner like Elijah in Matthew 11:10.
John 1:21: And they asked him, What then? Art thou Elias? And he saith, I am not. Art thou that prophet? And he answered, No. [that prophet: or, a prophet?]
Contradiction with Luke 1:76
Luke 1:76 describes John the Baptist as a prophet of the Highest, which supports rather than contradicts Matthew 11:10 by affirming John's role; however, it creates contrast when considering texts that deny his connection to prophecy like Elijah.
Luke 1:76: And thou, child, shalt be called the prophet of the Highest: for thou shalt go before the face of the Lord to prepare his ways;
Contradiction with Mark 9:11-13
Mark 9:11-13 indicates Elijah must come first and then recognizes him in John the Baptist but contradicts with the denial in other verses about John's identity as Elijah himself.
Mark 9:11-13: And they asked him, saying, Why say the scribes that Elias must first come?