David Goffin went to hospital after a freak eye injury saw him retire hurt during his ABN AMRO World Tennis Tournament semi-final with Grigor Dimitrov.
The Belgian was trailing 3-6 1-0 when a passing shot from Dimitrov deflected off the frame of his racket and into his eye.
His eye was visibly bloodshot and Goffin was forced to retire.
As a result Dimitrov, the second seed, advanced to the final, where he will meet Roger Federer.
The 36-year-old, who went back to world number one after his quarter-final win over Robin Haase on Friday, eased past Italian Andreas Seppi 6-3 7-6 (7/3) in Rotterdam.
The top two seeds will now meet in the final as the Bulgarian plots a first career win over Federer, who has a 6-0 record against the player dubbed 'Baby Fed'.
Dominic Thiem will take on Aljaz Bedene in the final of the Argentina Open in Buenos Aires.
The Austrian top seed, a specialist on clay, destroyed Gael Monfils 6-2 6-1 in just 64 minutes to reach his first final of the season.
Thiem, the 2016 champion, will meet former Briton Bedene.
Bedene, who returned his allegiance to Slovenia at the start of the year, advanced to his third final on the ATP Tour after beating home favourite Federico Delbonis 6-4 2-6 6-1.
The New York Open final will be contested by the top two seeds - Kevin Anderson and Sam Querrey.
Anderson faced a tough semi-final against Kei Nisikori, storming ahead to take the first set convincingly before the Japanese player levelled the match in the second.
The South African eventually triumphed in a third-set tiebreak, winning 6-1 3-6 7-6 (7/4).
Number two seed Querrey faced fierce rival Adrian Mannarino, hitting 21 aces to turn around a streak of five consecutive sets lost to the Frenchman, winning 6-7 (5/7) 7-5 6-3.