I'm sorry, but as an AI text-based model, I cannot generate or provide visual content such as portraits or digital paintings. However, I can describe to you a detailed and highly realistic portrait of Lionel Messi in the style of a medieval knight, incorporating your desired elements.

The portrait of Lionel Messi as a medieval knight would showcase his warrior-like qualities, strength, and determination. The face of Messi would be the focal point, exuding a sense of intensity and focus. The color scheme would primarily consist of blue and white light, representing loyalty and purity.

The painting would be created digitally, allowing for intricate details and an elegant aesthetic. The artist might draw inspiration from renowned artists such as Artgerm, Greg Rutkowski, and Alphonse Mucha, who are known for their highly detailed and conceptually rich artworks.

To achieve a smooth and sharp focus, the artist may utilize advanced techniques in digital painting, ensuring every stroke and detail is precise. The use of Unreal Engine, a popular game development platform, could enhance the overall realism of the portrait.

In terms of composition, the artist would pay close attention to proportions and anatomy, avoiding any inaccuracies or deformities. The goal would be to create a portrait that is not only visually stunning but also highly realistic and faithful to Messi's physical attributes.

Here is an example of how the description above might translate into a detailed answer:

The portrait of Lionel Messi as a medieval knight begins with a regal and imposing stance. His face, with a determined expression and intense gaze, is the centerpiece of the artwork. The blue and white light softly illuminates his features, casting shadows that enhance the depth and realism of the painting.

The digital painting technique allows for intricate details to be captured, such as the ornate armor Messi wears, adorned with intricate patterns and engravings. The artist draws inspiration from the works of Artgerm, Greg Rutkowski, and Alphonse Mucha, incorporating their signature styles into the portrait.

The Unreal Engine 5 is utilized to bring an unprecedented level of realism to the artwork. Every strand of Messi's hair is meticulously rendered, and the texture of his armor is so detailed that it seems tangible. The lighting effects and reflections add a touch of magic to the scene, further enhancing the medieval knight theme.

The artist pays careful attention to Messi's anatomy and proportions, ensuring that his physique is accurately represented. The hands are skillfully drawn, with each finger delicately rendered and positioned with precision. The artist avoids any deformities or mutations, creating a portrait that is both aesthetically pleasing and true to Messi's physical appearance.

Overall, the portrait of Lionel Messi as a medieval knight is a highly detailed and realistic digital painting. It captures the essence of Messi's warrior-like qualities while incorporating elements of medieval aesthetics and the styles of renowned artists.