U.S. stock index futures pointed to a lower open on Tuesday as investors awaited some minor data releases ahead of Friday's key jobs report, amid continued concerns about Greece.

A shopper loads purchases into his vehicle outside a Dollar General Corp. store in Princeton, Illinois.

Tuesday is a quiet day for U.S. data, with factory orders for April at 10 a.m. ET and auto and truck sales for May, which are released throughout the day.