LME copper for delivery in three months was at $3,943/3,948 a tonne by 0432 GMT, down from Tuesday's London close of $3,945. In Asia, copper remained in a range of less than $20 a tonne.
"I think there was some selling coming from China this morning," an LME trader in Tokyo said, noting some profit-taking after copper gained sharply on Tuesday.
On Tuesday, copper, used in construction and electronics, hit a high of $3,955 before closing up $89 or 2.3 percent at $3,945.
The Tokyo trader put support for copper at $3,920 and then $3,800/$3,750, with resistance at $4,000.
Copper prices were expected to test above $4,000 a tonne again because of high volatility in the market ahead of next week's November options expiry, he said.
A trader in Shanghai said a rumour surfaced on Tuesday that there would be some increase in Shanghai stocks this week, which added pressure on the market.
"But we don't know whether that's going to be true or not until Friday, of course," he said.
Last Thursday, copper hit a record high of $4,018 a tonne on strong Chinese demand, tight supply and speculative buying.
LME copper inventories fell 1,700 tonnes to 64,800 tonnes on Tuesday. Cancelled warrants, metal earmarked for release, accounted for more than 12 percent of total LME inventory, down from some 14 percent the previous day.
On the supply side, about 1,000 workers walked off the job at a major Grupo Mexico copper smelter and refinery, which principally serves the company's giant La Caridad mine, their union said on Tuesday.
Grupo Mexico called the strike illegal and said in a statement it hoped the federal authorities would act "in strict accordance with the law" to resolve the conflict.
A company official said Grupo Mexico was still analysing the extent of the strike, but said the La Caridad mine itself was unaffected.