ClipClapCat said: Is there anything wrong with the leaves or the stem?
That browning on the leaf is most likely due to lack of nutrients and the inability for root growth. Sometimes a young plant will get scars on the stem from the leaves moving in the wind and repeatedly hitting the stem. The scar will heal over faster with the proper growing conditions. A much larger pot with amended soil will most likely resolve all your issues. The cucumber is a fast growing sprawling vine that needs a lot of water and takes a lot of the nutrients from the soil to grow. Much more than is available in that small container.
