Lonhert has potential "Starter". He will reach his potential in two seasons of training and than you can either sell him or keep him, but if you advance in fourth league, I doubt he will be good enough for starting five; probably he will always start from bench.
This means you will spend two seasons to train a guy you won't need. I suggest you buy a new trainee. Nowadays, trainees with ~4k salary and perennial allstar potential go for really cheap.