World number one Andy Murray said he considered himself lucky despite seeing his season torpedoed by shingles, flu, an elbow injury.
Defending champion Novak Djokovic and Rafael Nadal were drawn to face each other in a blockbuster French Open semi-final.
“I think he can only improve, because he understands how strong he is.”
French Open director Guy Forget has said he was under no pressure to award a wildcard entry to two-times champion Maria Sharapova.
The French Open gets underway at Roland Garros on Sunday with a host of stars sidelined and others fighting races against time to be fit.
Roland Garros organisers are confident that the absence from the 2017 French Open of Roger Federer, Serena Williams and Maria Sharapova won't matter.
Kevin Anderson has booked his place in the quarter-finals of the Geneva Open, but he will have his work cut out to advance against Kei Nishikori.
World No 7 Thiem showed the blueprint for beating Nadal with a brilliant two-set performance in Rome.