Contradiction with Matthew 26:56
This verse states that all the disciples forsook Jesus and fled, which contradicts John 13:23 where a disciple is described as being close to Jesus.
Matthew 26:56: And they that had laid hold on Jesus led [him] away to Caiaphas the high priest, where the scribes and the elders were assembled.
Contradiction with Mark 14:50
This verse also mentions that all the disciples abandoned Jesus, which conflicts with the notion in John 13:23 that one disciple was leaning on Jesus.
Mark 14:50: And they all forsook him, and fled.
Contradiction with John 16:32
Here Jesus foretells that the disciples will leave Him alone, yet John 13:23 describes a disciple being in close proximity to Him.
John 16:32: Behold, the hour cometh, yea, is now come, that ye shall be scattered, every man to his own, and shall leave me alone: and yet I am not alone, because the Father is with me. [his own: or, his own home]