Nadal lost 6-4, 6-4 to go out at the semi-final stage of the ATP Tour 500 series event for the first time in his career.
The Spaniard is an 11-time champion in Barcelona and previously owned a 46-1 record at his tournament but fell to Thiem in a thrilling contest.
Thiem – who now has four clay-court wins over Nadal – advances to the final to face Daniil Medvedev.
Nadal, meanwhile, will prepare for the Madrid Open as he looks to collect his first title of the season on his favoured surface at the only clay event he failed to win in 2018.
This year, he has dropped out of both tournaments on the red stuff so far having lost to eventual winner Fabio Fognini at the Monte Carlo Masters.
But asked about his opponent, 25-year-old Thiem, Nadal insists he would love to watch the Austrian go on and become the world No 1.
Thiem is currently ranked fifth by the ATP having beaten Roger Federer in the Indian Wells Masters final back in March.
Asked if Thiem can become No 1 eventually, Nadal replied: “Why not? Depends. Everybody can be No 1.
“Well not everybody but there is a couple of players who can be No 1.
“It is not an easy thing. It depends on the results he will be able to have.
“He’s a good player, he’s a hard worker so I would love to see him play as No 1.
“I like him in all terms, he’s a hard worker as a tennis player and I like him as a person.
“I wish him all the very best for his future.”
Yet Nadal issued a warning ahead of any possible clay-court meetings with Thiem in Madrid, Rome or Roland Garros over the coming weeks, insisting that he wants revenge for his defeat.
The 17-time Grand Slam champion continued: “But not every thing, I hope to be ready to compete against him and to win against him in the next couple of weeks.”
Despite exiting the Barcelona Open before the final, Nadal insists he has still made positive progress in his homeland.
He added: “After this week I believe my confidence is back.
“I really believe I make very important improvements to create a good base for trying to achieve my goals during the next couple of weeks.”