The England international only started 20 Premier League games last season.
Oxlade-Chamberlain told the London Evening Standard: "Jack is back in training and looking really good. He is obviously coming away with us on tour today and the fact he is looking so strong is good news for Arsenal and England.
"Hopefully, he can stay fit because he is an amazing player and can add a lot to our team. Is he the best kind of signing we can make? Yes.
"Everyone is important. Whenever you lose someone it dents the team in some way. If we can keep him fit, it will give us a lot more options and enhances competition for places.
"One thing I have realised as he's gone through this, he is a much stronger character on and off the pitch. He has learned from it and has become a better man for it. He does a lot of stuff now to prevent these things from happening.
"He works really hard and is the first one in and last one out of training. To come through something like that, having not been able to play for 17 months and always stay positive, is really mentally challenging but he did that really well. Last season he had a good stint in the team and now he is pushing on again."