Zverev seriously injured an ankle in the French Open semifinal against Rafael Nadal in early June.
Since then he has been in rehab, a rehab that has now suffered a setback.
- I guess I pushed too hard (in rehab) and now I'm in extreme pain, says Alexander Zverev and continues:
- I have to be careful otherwise it could pose a danger for the future.
The idea was that Zverev, a former world number two who has slipped to fifth in the men's world rankings, would be involved when Germany play Davis Cup group games in Hamburg this week.
It won't be like that.
When he will be back is unclear.
- It is about weeks, probably months, to a competitive comeback, says Zverev.