The 30-year-old was expected to return to his former club Arminia Bielefeld this summer.
But that move has been shelved following interest from the Tigers.
"Delron is currently on trial with Hull City in England," Borussia sporting director Michael Zorc said.
Tigers boss Phil Brown is keen on adding to his squad with experienced players ahead of their first season the Premier League.
Buckley has struggled to hold down a first-team place at Dortmund since leaving Arminia in 2005.