US stocks were struggling for a direction ahead of Tuesday's opening bell as traders returned from a long holiday weekend, while concerns about the economic impact of coronavirus' delta variant persists. Dow Jones Industrial Average futures gained 26 points or 0.1%, S&P futures slipped less than 1 point or 0.01%, while Nasdaq futures were up 0.02%. Oil prices fell, with front-month global benchmarks Brent crude down 0.8% and US West Texas Intermediate crude down 1.5%, after top global exporter Saudi Arabia moved to cut prices for Asian customers. There are no major economic data due for release. In other world markets, Japan's Nikkei closed 0.9% higher, Hong Kong's Hang Seng closed 0.9% higher, and China's Shanghai Composite closed 1.5% higher. Meanwhile, UK's FTSE 100 fell 0.2% and Germany's DAX index slipped 0.1% in Europe's early afternoon session. On the winning side, shares of Aehr Test Systems (AEHR) were 1.8% higher pre-bell after the company secured a $19.4 million order for multiple FOX-XP test and burn-in systems. RenovoRX (RNXT) shares surged 45% after the company secured a US Food and Drug Administration 510(k) clearance for RenovoCath Delivery System to treat solid tumors. On the losing side, Forward Pharma (FWP) shares tumbled 16% after the European Patent Office dismissed the company's appeal against cancellation of multiple sclerosis drug patent.