Wimbledon finalist Nick Kyrgios was beaten in his first singles match since October after having knee surgery.

Elsewhere, American Venus Williams' return to grass-court action ended in defeat by Celine Naef at the Libema Open in the Netherlands.

The 42-year-old former world number one lost 3-6 7-6 (6-3) 6-2 to Naef, 25 years younger at 17 years old.

With her sister Serena watching on in the crowd, Williams, who was handed a wildcard for the tournament, started brightly to take the first set.

Naef took a closely fought second via the tie-break and she was then able to ease through the final set.

Williams was making her first competitive appearance since the Auckland Open in January, where she reached the last 16 before losing to China's Zhu Lin.

Williams has won seven Grand Slam singles titles - Wimbledon on five occasions and the US Open twice.

Kyrgios had not competed this season after having surgery to repair a small tear in his left lateral meniscus in January.

"I wouldn't say it was major surgery, but I had quite a serious surgery on my knee," Kyrgios said on Saturday. "It's taken me about five months to get back to even playing, moving and [ready to play] against these players.

"It's been difficult, but at times it's been amazing just to be home with my family.

"Tennis is a sport where you travel so much of the year and being home, for me, was important. But seeing everyone [else] play wasn't easy at times. I'm just super excited that my knee is a bit better and I'm able to play now."

Kyrgios reached his first Grand Slam singles final at Wimbledon last July, losing in four sets to Novak Djokovic. This year's Wimbledon tournament begins on Monday, 3 July.