The Swiss icon returns to the ATP Tour after losing to Rafael Nadal in the French Open semi-finals.
The Spaniard went on to win his 12th Roland Garros title by beating Dominic Thiem in the final to take his overall tally of Grand Slam triumphs to 18.
Nadal has a record 59 titles on the red dirt, on which he is known as the ‘King of Clay’ as the surface’s undisputed best ever player.
Roger Federer, meanwhile, is renowned for his achievements on grass with an Open Era-record 18 titles on the surface.
The 37-year-old has claimed a record eight Wimbledon titles as well as winning the Halle Open nine times.
Federer is looking to reclaim his crown in Germany after losing to Borna Coric in last year’s final and takes on John Millman in today’s first round, with the Australian having shocked the 20-time Grand Slam champion at the US Open last year.
And as he returns to the grass looking to claim a 10th Halle title and then a 21st Slam, Federer insists his feeling on the lawn is similar to Nadal’s on clay.
“I think it [grass] highlights my strength and it maybe hides my weaknesses,” Federer told the ATP’s official website.
“From that standpoint, I can play how I want, on my terms, how I would like.
“When you feel that way, it is maybe what Rafa feels on the clay. He can decide to return from back, he can return from in. I can do the same from grass, I can chip it, I can come over, I can serve and volley, I can stay back.
“I have all the options and when you have options, it gives you options to win and different tactics you can use against different players.
“That gives you maybe that little bit more margin you need to stay out of trouble and win matches.
“Then again the pressure is high for me too. The grass-court season is extremely short.
“There is not that much I can do to get into it as well, other than have that point-for-point mentality.
“The focus needs to be crystal clear and that is what I need to have from the get-go here as I play John Millman in the first round, who has been a tough one for me in the past.”
Federer has played Millman twice, losing to him in the US Open fourth round last year having beaten the Australian at the Brisbane International four years ago.