I wouldn't be too concerned. That is the second true leaf that came out, so by now its pretty old and is not getting much light at all. The plant will actually start to use up the nutrients in the old leaves at the bottom and use this to feed the top new growth. Looking at the top of the plant, it looks nice and healthy. I don't think there are any deficiencies going on. Just pluck those old leaves off and keep an eye on the new growth and leaves towards the top that are getting lots of light.