Jensen, 25, had a great start to the new season with eight goals in nine games across the Europa League qualifiers and Eredivisie.
After failing to fully control the ball in the first half against Bosnian outfit Zrinjski Mostar, Jensen stood on the ball and rolled his right leg over it, immediately grabbing his hamstring afterwards.
Initial tests indicated an absence of weeks, but after getting a second opinion, FC Utrecht communicated on Wednesday that Jensen will miss several months. The injury forced Jensen to withdraw from the Danish national team after his first-ever call-up.
"I am extremely disappointed that I will have to miss the upcoming European matches with FC Utrecht and my first call-up for the national team," Jensen said on the club website.
"It was a childhood dream, one that I will continue to work towards. I am happy that the team has done the job and qualified for the Europa League. In the coming period, I will do everything I can to be part of the team again soon."
FC Utrecht play their first Europa League game since 2011 on September 25th against Olympique Lyon in Utrecht.