The 17-time Grand Slam winner will play in Stuttgart from June 6th-12th, which is celebrating its 100th anniversary, before playing his next grasscourt tournament in Germany at Halle the week after.
The 34-year-old will be bidding for his ninth win in Halle in his warm-up for Wimbledon, which he has already won seven times.
The Swiss dropped out of the French Open at Roland Garros, which concludes this weekend, with a back injury.
In Paris on Thursday Swiss eighth seed Timea Bacsinszky was denied a second semifinal appearance by Kiki Bertens, who became the first Dutchwoman in 45 years to reach the French Open semifinal, winning 7-5, 6-2 over the Swiss.
There were seven breaks of serve in the opening set which ended with Bertens in control of the tie but needing to have her left calf strapped.
She raced into a 4-0 lead in the second set before Bacsinszky, who was to end the match with 40 unforced errors, briefly rallied.
But it was all too little, too late and Bertens' powerful, deep hitting gave her victory on a second match point.
In the men's draw, Swiss defending champion Stan Wawrinka plays Briton Andy Murray in the semifinal later today.
The 31-year-old Swiss is the oldest semi-finalist in Paris since Jimmy Connors in 1985.
Murray leads their head-to-head 8-7 but Wawrinka has won their last three meetings.
The third seed has also won both their tour claycourt meetings — in Rome in 2008 and Monte Carlo in 2013.
However, Wawrinka insists that Murray is the favourite, even claiming that the Scot is in a different class despite both men having claimed two Grand Slam titles apiece.
“If you were to compare our two careers he's well ahead of me given all the titles, the finals, number two in the world, and he has so many Masters 1000, as well,” said Wawrinka who was also the 2014 Australian Open champion.