NEW YORK (TheStreet) -- Stock futures traded slightly higher on Friday but steep market declines in China and concerns over Greece's debt woes could make for a volatile session.

S&P 500 futures added 0.18%, Dow Jones Industrial Average futures gained 0.20%, while the Nasdaq rose 0.05%.

The Shanghai Composite fell 7.4%, amid worries that Chinese equities are overvalued. Japan's Nikkei 225 index and Hong Kong's Hang Seng also posted losses.

Greece and its creditors were unsuccessful in agreeing to a debt deal, despite three meetings this week. Talks are set to continue on Saturday. The clock is ticking, as Greece has a payment due to the International Monetary Fund on June 30.

Back in the U.S., investors braced for a rebalancing of the Russell 2000, an index of small-cap stocks.

"[Friday] will almost certainly be the busiest trading day of the year, as the Russell indexes go through their annual rebalancing/reconstitution," Nicholas Colas, chief market strategist at Convergex, wrote in a note. "But Friday's close will be the end of a trade that began almost 2 months ago, as traders began handicapping which equities would be included for the first time or swapped between various Russell indices."

U.S. investors also await key consumer sentiment data, released at 10 a.m. EDT.

Valeant Pharmaceuticals (VRX) made an offer to acquire Zoetis (ZTS), an animal-health company, sources told The Wall Street Journal, which said it's not clear what "the company's reaction to the approach was, if any, or whether it is open to a sale." Shares of both companies moved slightly lower in premarket trading on Friday.

Micron (MU) shares dropped 14.4% in premarket trading, after quarterly earnings and revenue fell short of analysts' estimates.

Nike (NKE) shares saw a boost in premarket trading, trading up 3.9%, following better-than-expected fiscal fourth-quarter earnings. The athletic equipment and apparel company posted earnings per share of 98 cents, topping analysts' estimates by 15 cents.

Canadian fertilizer company Potash (POT) were down about 0.30%, but closed higher by almost 5% on Thursday, following reports that it's looking to merge with K+S, a fertilizer company based in Germany.

Shares of athletic retailer Finish Line (FINL) soared 4.7% in premarket trading, after the company's sales and profit beat Wall Street's estimates. The company posted earnings per share of 30 cents, beating estimates of 24 cents.

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