How many 20 years old costs 20million? At that price he should be compared to a young Ronaldo - but he's shown that he's not even half the player an 18 year old Ronaldo was when he first came to England.
I'm not sure why some are comparing him to Henderson. They play different positions. Henderson plays in a position that arguably could be trained and worked on. Markovic plays in a position that, in order to be successful in the premier league, requires flair, instinct, guts, first touch, skills, vision and shooting. Very few of these attributes can be trained and you need to already HAVE it to be here. Ronaldo had all of them and he trained on his shooting and skills to become the world class player he is.
Markovic on the other hand showed none of these attributes (so far). It's laughable to expect anything more of him - it's like picking some random sod off the streets and expecting them to train and come good. We are persisting with him only because he cost us 20million which will raise many questions on our scouting. I hope I'm proven wrong and BR is seeing something in him that I don't by continuing to play him.