Wong said he had left the city after being physically attacked by masked men in Wan Chai two weeks ago.
He didn’t reveal where he had travelled to and said while it was a “one-way trip”, he is praying he will be able to return to the territory one day.
In a letter to the university’s governing council, Wong said he fears for his life and those of his relatives, because of the attack, and now that Hong Kong has become “a police state”.
He added that he will forever feel ashamed to have left Hong Kong during this “critical time” amid the ongoing anti-government protests.
Wong had recently been involved in organising class boycotts by university students as part of the anti-extradition bill campaign.