Roger Federer "has a clear picture" of his fitness heading into Wimbledon after a run to the semi-finals at the Gerry Weber Open.

Federer, who is recovering from a back injury that forced him to miss the French Open, lost 7-6 (7-4) 5-7 6-3 to Alexander Zverev and looked leggy at times against his vibrant opponent, but the Swiss star insists he is returning to his best form.

The 34-year-old had won the Halle event on eight previous occasions, but found Zverev's energy and consistency a step too far after earlier victories over David Goffin, Malek Jaziri and Jan-Lennard Struff in Germany.

"Looking back on how I felt three, four weeks ago, this is pretty good," Federer told reporters after the match.

"Talking to me after a loss clearly is always tougher to step back and just to reassess how great everything is, but I must say it's gotten better and better.

"I think there are little things that just have to fall into place and then you play better and feel better. I hope it's sooner than later and I know what I need to work on in the next 10 days. Clearly, I also need to rest now. It's been a lot of tennis.

"This has been seven matches in nine or 10 days now. It's been intense and it's been busy and it's exactly what I needed. At least I have a clear picture now where my game is at, what I need to do and without Stuttgart and Halle I wouldn't have that. I have more clarity now."

Federer also lost in the semi-finals of his last event, the Stuttgart Open, to Dominic Thiem, but insisted he is satisfied with the state of his game.

"The only thing missing is a better baseline game. I guess that comes through movement and through just playing enough again," said Federer. "I feel the serve has come back around now, the returns have gotten better also throughout the match today.

"I think if the movement gets better and then the baseline game improves a little bit, I'll be better on the big points, on the return and also in less trouble on my own service games.

"But I'm okay and I'm pleased on how I played, how I'm feeling and now we've got enough time before Wimbledon to get ready for that."