The 17-year-old has been dubbed ‘The Little Kaka’ in the press.
“It is not true that Ljajic went to England without permission,” the club’s general secretary Darko Gubor told nogomet.com.
“We have been in contact with Manchester United for some time now and Ljajic was with the international team in Britain at this moment so it was handy for him to go on trial now.
“We want to co-operate with Manchester United and this is only the first step.
“I repeat Ljajic went to Manchester with Partizan’s permission and all I can say regarding his potential move to United is that he is still a very young player who is at the beginning of his career.”