We do not know for sure whether John knew the story of the Last Supper as we find it in the synoptic gospels and in 1 Corinthians 11. However there is considerable evidence that John had some understanding of Christ’s presence and power in some kind of eucharist—look at John 6, and the reference to the vine in John 15, and—written perhaps a little later than the rest of the gospel—the resurrection meal in John 21.
Therefore what strikes us here is that in his account of the Last Supper John says nothing about the institution of the Eucharist or Lord’s Supper. The disciples are there; a meal is served; Judas gets ready to betray his master.
But instead of the words about the bread and wine we get another highly symbolic act—the washing of the disciples’ feet—and a command: that they serve one another in the same way.
It may be that the footwashing is a reminder of another fundamental rite of Christian belief—baptism. (See the references to water in the Nicodemus story of Chapter 3 and the blood and water that flow from Jesus’ side in John 19:34).
What is quite clear is that the act of footwashing provides the opportunity for Jesus to declare John’s own version of the great commandment: “that you love one another. Just as I have loved you, that you love one another.” (Jn. 13:34)
Notice too that the story of the Last Supper continues for three more chapters as Jesus prepares the disciples for life after he leaves—life with the Spirit he will send.