The Venuezuelan striker has not started a game for Celtic in their last four matches, and has yet to net his first goal for the Hoops.
The form of Gary Hooper has meant Miku has found it difficult to find his way into Neil Lennon's plans.
And the on-loan Getafe ace has revealed he is frustrated at the way his time at Celtic has started.
He said: "Yes, I am a little worried about the situation. It's a season-long loan and I am happy in the sense that we are playing in the Champions League and we can win a title and, of course, that's always important.
"However, on a personal level, I was expecting this to be a big year for me and to take a leap in my career to a new level of quality.
"But I have to be calm because there is still a long time left of my deal."
Miku revealed Lennon has given him a pep talk about why he has not used him so far.
He said: "Every day is a new challenge for me in Scotland. Physically, football is different from what I was used to. If you cause a foul in Spain, it's a yellow card, here it's play on.
"The manager has spoken to me and told me that technically, I'm the best player we have, but physically I'm not ready to compete in Scottish football and I have to be patient and wait my time.
"I was happy with that assessment, because it is something that gives me encouragement. However, I want to be more involved.
"The truth is that it is hard for me now because I am not being used and this is a new situation for me.
"I am finding it hard to adapt at the moment, but that's football for you.
"One day you are playing and the next you can be a back-up. I will have to work hard to reverse this situation. I admit it has been difficult here so far."