Second seed Gael Monfils withdrew from the San Jose Open tournament on Friday after defeating American wild card Tim Smyczek 6-4, 7-6 in the quarter-finals.
The Frenchman aggravated an injured left wrist in his win over Robert Kendrick on Thursday and after beating Smyczek a day later, determined he was unfit to continue.
"It's been a month-and-a-half that I've had this pain," Monfils said. "I can't hit my backhand. I tried, but my backhand is very soft. I have a better backhand than I showed here... more powerful."
Monfils has subsequently withdrawn from tournaments in Memphis and Acapulco and a Davis Cup tie, and is expected to miss up to six weeks of action.
Elsewhere, top seed and defending champion Fernando Verdasco broke once in each set to record a 6-4, 6-4 win over fifth seed Denis Istomin.
"I tried to play a game he doesn't like, with a lot of spin, and it went well," the Spaniard said.
"I played well on the important points, like I did yesterday, which was good too. I knew it would be tough. Denis made it to the semi-finals here last year and the conditions benefit him."
Juan Martin del Potro continued his comeback from a wrist injury that sidelined him for a year with a comfortable 6-2, 6-3 win over Lleyton Hewitt and the Argentine will next face Verdasco in the only semi-final to be played on Saturday.
In form Canadian Milos Raonic advanced to the final four with a 6-4, 7-6 victory over Richard Berankis and is guaranteed a place in the final following Monfils' withdrawal.
Soderling beats Youzhny to stay on course for title
Top seed Robin Soderling beat Mikhail Youzhny 6-4, 7-6 in a reprise of last year's final to reach the last four of the world indoor tournament on Friday.
Defending champion Soderling will now meet unseeded Viktor Troicki of Croatia, a 7-5, 6-2 winner over Marin Cilic, on Saturday.
Soderling, who hit 13 aces, finished off the first set with a break. When Russian Youzhny wasted a chance to take the second set, the Swede struck in the tie-break.
"It was a tough match but so far all my matches this tournament haven't been easy," Soderling told reporters. "Today I felt really strong on the big points and that gave me confidence."
Earlier, Ivan Ljubicic beat Cypriot Marcos Baghdatis 6-4, 6-7, 7-6 to reach the semi-finals where he will face Jo-Wilfried Tsonga, who had a day off as his opponent, Tomas Berdych, pulled out with influenza.
Dolgopolov faces top seed Almagro in Brazil Open final
Red-hot Ukrainian Alexandr Dolgopolov reached his first ATP tour final when he brushed aside Ricardo Mello 6-2, 6-1 in the Brazil Open on Friday.
The Australian Open quarter-finalist will meet world number 13 Nicolas Almagro in Saturday's final after the Spanish top seed overcame Argentina's Juan Ignacio Chela 1-6, 6-2, 6-4 in the other semi-final.
Top seed Almagro will be looking for his second Brazilian title after winning the tournament in 2008. The 25-year-old has enjoyed considerable success on Latin America's claycourts having also won the Mexican leg of the four-tournament circuit in 2008 and 2009.