Serena Williams, who will be playing an exhibition match against her good friend Caroline Wozniacki in Herning, Denmark, says that the Dane can win multiple Grand Slams.

A former No. 1, Wozniacki ended her 2015 season at No. 17, her lowest ranking since 2007. She was ranked No. 1 back in 2010 and 2011. The 25-year-old reached the 2014 U.S. Open final, losing to Williams, in her only major final appearance.

“She has even been able to be No. 1 in the world for more than a year and [that] should be something to put more focus on rather than to note that she has not yet won a Grand Slam tournament,” Williams said.

This season, Wozniacki has gone deep at some of the smaller tournaments—reaching the final of Auckland, winning Kuala Lumpur, and reaching the semifinals in Eastbourne and New Haven. But other than reaching the final in Stuttgart, she lost early at all the majors and the WTA Premier events.

The Dane lost in the second round of the Australian Open, French Open and U.S. Open (losing to Victoria Azarenka, Julie Goerges and Petra Cetkovska, respectively). At Wimbledon, she reached the fourth round before losing to eventual finalist Garbine Muguruza.

However, Williams believes that Wozniacki can play better in 2016.

"Caroline is very young," Williams said, "And she still has a great chance to do everything she can to win not just one—but many Grand Slams. Tennis is an interesting game. You see players who sometimes perform extremely well, and you never know what can happen. Caroline is at a level where there are so many good players, including herself."

It was the first time that Serena has spoken in a press conference since she lost in the semifinals of the U.S. Open.