Klopp, who has previously been linked with Arsenal and Manchester United, announced his Dortmund contract would be cancelled at the end of the season, sparking talk of another Premier League move - this time to Manchester City.
Retired Germany international Mertesacker, who racked up 104 caps, feels the Bundesliga's loss will be the gain for wherever the two-time German football manager of the year ends up.
Mertesacker also declared his hope more German tacticians move abroad, with only Felix Magath - Fulham's manager for 12 doomed top-flight matches in 2014 - previously flying the flag in the Premier League.
"It's obviously sad news for Borussia Dortmund - such a successful and passionate manager for them - he was the guy that turned it around at Dortmund," Mertesacker said.
"The whole situation there - he built the squad on young players, and they improved so much in the last seven years he was in charge, so it's a sad situation.
"In the summer it's a new situation for him.
"Maybe he's going to take a challenge and go abroad and see how it goes. I would love to see more German managers abroad, because it's obviously a challenge to learn the new culture, the new language, to adapt to a different system. Why not?
"But it's his decision and he worked really hard, and pushed really hard, so even if he says he's not tired, I think maybe taking a little break and a little breather, would help him to fuel his energy and his batteries.
"I am curious what will happen to him, because he was an outstanding figure in the Bundesliga in the last couple of years - always a title contender, they went to the Champions League final [in 2012-13].
"It'll be interesting to see what happens in the summer."
