"Obviously last season ended brilliantly for the team and for myself, and it's good to be back, but I'm not really looking forward to pre-season training," he told ManUtd.com.
"Wednesday was just testing to see where your fitness is at. Thursday is another treadmill fitness test which will be quite hard, and that will start to build things up. I'm not really looking forward to it, but you've just got to get through it haven't you?
"Long distance running gets easier as you get older, I think, it's just the quicker stuff that is quite hard. But you've done it all before and just use your experience to get through it."