European markets opened more than 1 percent lower in early trading, though they clawed back some territory later in the morning and were hovering at about half a percent lower, with the benchmark Stoxx Europe 600 down about 0.3 percent.
Futures tracking the S&P 500 predicted a drop of about 1.1 percent when trading starts later in the morning.
Adding to the downbeat mood in markets, the U.S. Labor Department’s jobs report for September, to be released later Friday, is expected to show that while employers continued to return employees to work, the improvement in the labor market is losing momentum.
The news of Mr. Trump’s health pushed prices for United States Treasury bonds higher, sending yields lower. Gold prices also rose, as did the value of the Japanese yen against other currencies. These are all traditional haven assets that investors buy when they want to reduce risk.
Oil futures slid, with Brent crude and West Texas Intermediate, the two main benchmarks, down about 3 percent. Prices for other commodities fell too.