It's not natural and it's not correct grammar. To fix the grammar and make it smoother, you could say: "He was pretending to be sick, to draw her attention" or "He was pretending to be sick just to draw her attention" or you could say "He was acting sick..." which is a bit more efficient.

“He was pretending to be sick to get her attention” would be a more common way to say it

Dan has it completely correct with each of his 3 options.

It sounds ok for me.

"He is pretending sick" makes logical sense, but is grammatically wrong. The reason it makes logical sense is that he is pretending the state described by the adjective "sick". It is reasonable to suppose that the adjective "sick" might be usable and say "he is pretending sick". Alas, you cannot do that. You can only pretend a NOUN: "He is pretending NOUN", or "He pretends NOUN". One simple way to do this correctly is to use the noun "sickness": "He is pretending sickness", or "He pretends sickness". Another approach is to find a noun phrase that names the state of being sick. The two most natural ways to do this are "He is pretending to be sick", and "He is pretending being sick". The first choice is better because it avoids using two consecutive present participles, but both are correct. The thing that makes this work is the fact that "being" and "to be" can both be used as nouns. ALL infinitives and present participles can be used as nouns. Here are some other ways to say this: "He is making believe that he is sick." "He is feigning sickness" (better than "pretending") "He feigns sickness". (better than "pretends") "He is acting sick". ("sick" describes him) "He is acting sickly". ("sickly" describes "acting")