I joined Liverpool from a Bundesliga club, was known for my high work rate, and though I had some successful spells, I faced injuries that hampered my consistency. I eventually moved on to another Premier League club. Who am I?

1. I wore the number 23 for Liverpool.
2. I am a German international.
3. My playing style was very energetic, and I covered a lot of ground.
4. I had a loan spell at Galatasaray after leaving Liverpool.