In the midst of what could be the final match of Rafael Nadal's career, Serena Williams shared a message to a fellow legend of the tennis court.

In a post on X, Williams noted she was getting choked up while watching Nadal play for Spain in the Davis Cup on Tuesday.

Williams' post is the second message Nadal received from a legendary peer. Roger Federer wrote a letter to his longtime friend and rival on Tuesday.

Nadal announced on Oct. 10 that he would be retiring from tennis, with the Davis Cup serving as his farewell event.

Speaking to reporters on Monday, Nadal admitted he wasn't sure of his role on Spain's Davis Cup team.

"If I'm on the court I hope to control my emotions. I'm not here to retire, I'm here to help the team win," Nadal said. "It's my last week in a team competition and the most important thing is to help the team. Emotions will come at the end. Before and after I'll be focused on what I have to do."

Spain captain David Ferrer announced would play in the No. 2 singles spot against Botic Van De Zandschulp of the Netherlands in a quarterfinal match. If the Spanish team were to advance to the semifinals, it's possible Nadal would play at least one more time.

After Williams announced the 2022 U.S. Open would be her final tournament, Nadal praised her for all the things she did on and off the court:

"She is one of the greatest sports [people] of all time. I feel lucky to share a tour for a long period of time with her. Of course, from a selfish point of view, it's sad that she's leaving the tour but, on the other hand, we can't thank her enough for all the things that she did for our sport."

At the time of Williams' retirement, she and Nadal had won the most grand slam singles titles during the Open Era. She still ranks first among all women's players with 23 titles. Nadal's 22 titles have since been surpassed by Novak Djokovic for most among men's players.