The Sherlock Holmes star works out with his sifu whenever he can and insists he can at least boast he's a good apprentice.
The actor tells Men's Fitness magazine, "I'm testing for the brown sash next. I've been doing it for eight years and I am now just approaching the halfway mark, grading-wise, which is great.
"That is an apprenticeship. Doing something for a year or two and being a black belt, to me, is something else. I also respect it and I am sure you have to work for it, but an apprenticeship takes a very long time.
"I guess in another eight to 10 years, I might know what I'm doing."