Despite finishing last season as the Bundesliga's top goalscorer with 25 goals, the Bayer Leverkusen forward has not appeared for the national team in over three years.
He has picked up only six caps and is yet to score for Germany, while he was not included in the latest squad for a friendly with Paraguay on Wednesday.
But Bierhoff says a route into the national team is always open for the 29-year-old.
"It always hurts to see players making a name for themselves, but not really making the step into the national team," he told Sky television.
"During my time, that was Martin Max. Joachim Low has said that all of the doors are open and it's up to the player to force his way in."
Kiessling seems intent on doing that too as he opened his account for the season in Leverkusen's 3-1 win over Freiburg on Saturday.
"It was great. We played a great game and showed excellent focus," said Kiessling.