The Sun says the former Feyenoord midfielder is trialling with United after he impressed turning out for Oldham last month.
Martis said: “I went into Leicester for a day and felt comfortable and got an offer.
“Then I went into Manchester United for a week and received good feedback from Warren Joyce and could have earned a deal had I waited, but I just want to get my career started.
"I am confident in my ability. I've played a number of games to obtain fitness and have done well."