Ferrer, 37, will retire from the tennis tour after the Madrid Open next month.
He waved his penultimate farewells at the Barcelona Open earlier today when he was beaten by Rafael Nadal in the third round.
The two Spaniards were emotional as Ferrer walked off centre court to a standing ovation.
And Nadal wishes his good friend would have won a Grand Slam in his career – the closest he got was a 2013 French Open final appearance.
But those major tournaments have been dominated by Federer (20 titles), Nadal (17), Djokovic (15) and Murray (3) for almost two decades.
“He has always been a rival who demands the maximum,” Nadal said of Ferrer
“Although the head-to-head is very favourable towards me, our matches have been very difficult.
“I think he has had a bad time.
“I’ve helped him improve, David is one of the most regular players I’ve ever seen and he’s always played at a very high level, except when he’s met the Big Four.
“It’s that in big tournaments, if he wanted to win it he had to beat at least two of them because we talked about players who never failed.
“It’s one of the things that I do not like, because he’s one of the players who deserve a lot more than what he’s achieved.
“By level of play and by human quality. Big Four, for me, has been the most regular player in recent years.”
Nadal also spoke of the amazing moments he had with Ferrer throughout his career.
“I have many, if I’m honest, maybe the most exciting moment together was the Davis Cup final in Seville, I think in 2011,” he added.
“Being a great team-mate, in team competition was life insurance.
“You knew that I was not going to fail you, he was always going to give the maximum.”