World number seven Dominic Thiem reached an Indian Wells Masters semifinal showdown with Milos Raonic without hitting a ball on Thursday as injured Gael Monfils withdrew.
France's Monfils, ranked 19th in the world, pulled out shortly before his scheduled quarterfinal against Thiem with left Achilles tendon trouble.
Monfils said he'd felt discomfort in his ankle for a couple of days and had been receiving treatment, but the pain was worse after his fourth-round win over Philipp Kohlschreiber on Wednesday night.
"I tried a little jog this morning, and I couldn't really actually push on it," he said. "Then we taped it. Then I hit a little bit tonight, and I felt that I cannot be 100 per cent. I have this pain, and it wasn't the right choice to play."
He said an ultrasound exam confirmed severe inflammation, and he wasn't yet sure if it would prevent him from playing the upcoming Miami Masters.
Thiem is through to the semifinals at Indian Wells for the first time, having reached the quarters once before in 2017.
Raonic ended the dream run of lucky loser Miomir Kecmanovic, beating the 19-year-old Serbian 6-3, 6-4.
Raonic, ranked 14th in the world, fired 13 aces and broke Kecmanovic once in each set to keep his bid to better his 2016 runner-up finish on track.
Raonic's serve wasn't at it's booming best. He put only 55 per cent of his first serves in play.
"I think that can get better," Raonic said. "But there are other things I'm doing well, for sure. As soon as I had a chance on the first forehand, I was able to find my way to be the one dictating the point."
Roger Federer and Rafael Nadal will be vying to set up a blockbuster semi-final when the play in the other two quarterfinals later on Friday.
A slew of errors came at the worst possible time for Venus Williams on Thursday as she blew a first set tiebreak before losing 7-6 (3), 6-3 to Angelique Kerber in the quarterfinals.
Momentum swung firmly in Kerber's favour during the tie-break when Venus committed six unforced errors, including a backhand into the net that handed the German the set.
The match, which featured two former world number ones, ended when Venus sent a backhand long on match point.
Kerber will play Switzerland's Belinda Bencic, whose resurgence continued on Thursday as she advanced with a battling 6-3, 4-6, 6-3 win over fifth-ranked Karolina Pliskova.
Bencic, a former world number seven whose ranking slumped as injuries stalled her career, took her current winning streak to 12 matches.
Six of those wins have come against top-10 players, including a 6-3, 6-1 triumph over world number one and defending Indian Wells champion Naomi Osaka in the fourth round.