Juan Martin del Potro climbed back to No. 11 in the rankings in 2017 and could keep rising, says his coach, Sebastian Prieto, but needs to keep up his level for 2018.

Del Potro was in contention for the ATP Tour Finals, but even though he didn't qualify, his coach said that the former 2009 US Open champion had a very good year and is ‘fully fit.’

“I am finding him a very calm person, relaxed on a day-to-day basis, but focused and strict with himself in terms of work. He is a top player in terms of work ethic and mentality,” Prieto told TenisZone, speaking in an interview.

Del Potro had three left-wrist surgeries between 2010 and 2015. Afterwards, his couldn't do much except a backhand slice. Now, he can hit his two-handed backhand with pace again.

Prieto began working with Del Potro just before the US Open. Since then, he has begun playing more consistently. First, the 29-year-old reached the semifinals at the US Open, upsetting Roger Federer in the quarterfinals, then tn the fall, he reached the final in Basel, and won Stockholm.

“I think the goal is for him to be physically healthy and compete in good form for the whole year. The...pre-season is important as it provides a good base for the whole season. He should play like he did in recent times, for the whole year.”

Del Potro will begin his season at the ASB Classic in Auckland.