Liverpool's campaign promised so much after their stunning 4-0 rout of Arsenal in August but Klopp's men have struggled since then, winning just one of seven matches in all competitions.
"I'm following Jurgen Klopp really closely because of the seven years we had when he coached me at Borussia Dortmund," Hummels told Sky Sports News .
"I was really happy when he had a good start this year, but right now it looks a little tough for him and the club.
"But he and the team will get out of this situation, it's not too bad but it's not as good as they wanted it to be."
Klopp has been linked with Bayern, who sacked head coach Carlo Ancelotti last week.
Bayern are yet to appoint a replacement, though former boss Jupp Heynckes – who orchestrated the treble in 2012-13 – is reportedly set to return on an interim basis.
"Munich talked to me and asked me something, I said my opinion," Hummels added.
"But I don't know if [former Dortmund boss Thomas Tuchel] is the most likely candidate for the job, or if there are one or two others. I have no idea.
"I will be as curious as all of us, reading newspapers to see what's going to happen."