The 23-year-old returned to training for the Foals, with whom he has a contract until 2017, keen to put two disappointing seasons behind him.
He only managed to find the back of the net six times in his first Bundesliga season, while he drew a blank in all of the last campaign, both in Germany and in England.
Having not scored since April 6, 2013, De Jong is desperate to prove himself at Gladbach but admits he may have to wait his turn.
"I would prefer to stay with Borussia," he said on the Bundesliga club's website.
"I've always said how fantastic a club Borussia are.
"I've also got to be realistic, though, and wait to see how my chances of playing look. I just want to be playing football again."
De Jong joined Gladbach for a club-record fee of 12million euros in 2012 after scoring 25 goals in 31 games for FC Twente in Holland.