* Comcast prepares all-cash bid for Fox assets
* Citigroup rises after ValueAct raises stake
* Trump to decide on Iran nuclear deal at 2 p.m. ET
* Futures down: Dow 0.15 pct, S&P 0.21 pct, Nasdaq 0.2 pct (Adds comments, details, updates prices)
By Medha Singh
May 8 (Reuters) - U.S. stock indexes were on track to open lower on Tuesday as investors braced for President Donald Trump's decision on whether to withdraw from the Iran nuclear deal.
A U.S. withdrawal would tighten economic sanctions on Iran, curtailing the country's output that could bolster this year's 13 percent oil rally.
Crude prices were down about 1 percent - easing from 2014 highs, which had boosted Wall Street in the past two sessions - ahead of Trump's decision at 1800 GMT (2:00 p.m. ET).
"(Trump's decision) has been so well covered, it's probably all in the price by now. And most recent commentary seems to be that after all the bluster, he may only partially withdraw from the deal," said Frances Hudson, global thematic strategist at Aberdeen Standard Investments.
At 8:33 a.m. ET, Dow e-minis were down 37 points, or 0.15 percent. S&P 500 e-minis were down 5.5 points, or 0.21 percent and Nasdaq 100 e-minis were down 13.75 points, or 0.2 percent.
"Depending on the magnitude of energy markets being affected, it could spillover to the rest of equities in general," said Andre Bakhos, managing director at New Vines Capital LLC in Bernardsville, New Jersey.
Shares of Comcast fell 1.8 percent premarket after Reuters reported the cable operator is preparing to make an all-cash offer for media assets that Twenty-First Century Fox has agreed to sell to Disney for $52 billion.
Fox's shares rose 2.4 percent. Disney, which is due to report its results after markets close, was down 0.7 percent.
Snap Inc gained 1.6 percent after hiring Tim Stone, who had led Amazon's $13.7-billion integration with Whole Foods, as its chief financial officer.
Dish Network dipped 1.2 percent after its quarterly revenue came below expectations due to a drop in its legacy pay-TV subscriptions.
Citigroup advanced 1.8 percent after activist investor ValueAct invested $1.2 billion in the bank, citing its low risk and reliable revenue. (Reporting by Medha Singh in Bengaluru; Editing by Anil D'Silva)