U.S. stocks looked set for a slightly lower open on Tuesday as investors readied themselves for an interest rate hike next week. 

The Federal Reserve has left no stone unturned in preparing the markets for tighter monetary policy when it meets on March 14-15. Central bankers could also call for faster rate hikes as the U.S. economy strengthens.

The chances for a rate hike this month are at 83 %, up from roughly 30 % at the start of last week, according to Thomson Reuters data.

"The market is headed for another slow mixed to negative session as investors continue to focus on an upcoming rate hike" Peter Cardillo, chief market economist at First Standard Financial wrote in a note.

While a post-election rally has been accompanied by pauses, the indexes have not experienced a steep correction, leading some to question market valuations.

The S&P 500 is trading at about 18 times forward earnings estimates against the long-term average of about 15 times, according to Thomson Reuters data. The index has not recorded a 1 % pullback since October.

Dow e-minis were down 28 points, or 0.13 % at 8:30 a.m. ET (1330 GMT), with 17,341 contracts changing hands.

S&P 500 e-minis were down 4.75 points, or 0.2 %, with 110,229 contracts traded.

Nasdaq 100 e-minis were down 10 points, or 0.19 %, on volume of 17,439 contracts.

Healthcare stocks could be in focus after Republicans unveiled a proposal on Monday that would roll back extra healthcare funding for the poor and introduce a system of tax credits for people to buy insurance.

Newly minted shares of Snapchat owner Snap Inc fell 3 % to $23.10 in premarket trading after a group representing large institutional investors asked stock index providers to bar the company and others who sell non-voting shares from their stock benchmarks.

Nimble Storage soared nearly 45 % after Hewlett Packard Co said it would buy the data storage provider for $1.09 billion in cash.

Dish Network was up 5 % at $64.30 after the satellite TV company was picked to join the S&P 500.