British number two Kyle Edmund had an injury scare as he pushed world number three Grigor Dimitrov to three sets in the quarter-finals of the Brisbane International.
The 22-year-old needed treatment after he went over on his right ankle at 4-4 in the decider.
He was able to resume but went on to lose 6-3 6-7 (3-7) 6-4.
Edmund will now have the injury assessed before 2018’s opening Grand Slam, which starts on 15 January.
With Andy Murray already out with a hip problem, Edmund is due to be the highest-ranked Briton in the men’s singles.
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He crashed to the ground with a scream after being wrong-footed by Dimitrov during a rally. After seeing Edmund’s distress, Dimitrov immediately leaped over the net and sprinted to his aid, helping the Briton to his chair.
“At the end of the day it’s health above all,” said Dimitrov. “It’s very unfortunate what happened. I’ve seen this too many times, I know the feeling and I really hope he gets better.”
Edmund’s ankle was taped up and he appeared reasonably comfortable on his return to the court, but the momentum had gone and two games later the match was over.
The Briton had looked solid in the opening set and had break points to go 4-3 ahead. Dimitrov saved both and in the next game the Bulgarian took advantage of a couple of errors to break for a 5-3 advantage, before serving out the set when Edmund netted a backhand.
Edmund had to save two break points in the ninth game of the second set and, encouraged, he swept through the tie-break to deservedly level the match.
The deciding set was equally close with Edmund saving two break points in his opening service game but he was unable to seal a first win in 14 attempts over a top-10 ranked player.
Dimitrov will face Australia’s Nick Kyrgios in the semi-final after he overcame Ukraine’s Alexandr Dolgopolov 1-6 6-3 6-4. The other semi-final will feature another Australian, 18-year-old Alex De Minaur, and unseeded American Ryan Harrison – who had been due to play Murray on Thursday before the Briton withdrew from the tournament.
BBC Sport tennis correspondent Russell Fuller
Edmund was matching the world number three shot for shot, until he lost his footing with the deciding set locked at 4-4.
Dimitrov’s instinctive reaction will live in the memory: a quick sprint hurdle and he was helping Edmund to his feet. Edmund had his ankle heavily strapped, and played on – but the shock of the fall did affect his composure as he was broken in the final game of the match.
Edmund expects soreness for a couple of days, but will fly to Auckland for next week’s event as planned.