* Wall St slips as Nike, UnitedHealth drag
* U.S. bond yields firm in light, pre-Christmas trading
* Euro slides as pro-independence Catalan parties win seats
* Spanish bond yields hit over 1-month high
* Bitcoin plunges below $12,000, heads for worst week since 2013 (Updates with U.S. afternoon trading)
By Laila Kearney
NEW YORK, Dec 22 (Reuters) - Major global stock indexes slipped slightly on Friday as a drop in shares of Nike and UnitedHealth helped offset any gains, while Spanish bond yields rose and European stocks briefly stumbled after separatists prevailed in a Catalan election.
Nike shares dropped more than 4 percent after it forecast muted current-quarter revenue growth, highlighting its struggles to regain market share in North America from Adidas.
UnitedHealth slid 0.7 percent after the health insurer agreed to buy Chilean healthcare company Banmedica SA for $2.8 billion.
Despite the dip, Wall Street was poised to end the week higher after rallying sharply ahead of a $1.5 trillion tax cut bill that passed in Washington on Wednesday. U.S. President Donald Trump signed the tax overhaul into law on Friday.
Stock markets around the world shot higher as the law, seen as boosting corporations and leading to economic growth, advanced through both chambers of the Republican-dominated Congress.
"We're in a bullish phase and investors have things to feel good about," said Andres Bakhos, managing director at Janlyn Capital LLC in Bernardsville, New Jersey.
Investors were also winding down ahead of the Christmas holiday on Monday.
"Volumes in the stock market are down 28 percent," said Michael Antonelli, managing director, institutional sales trading at Robert W. Baird in Milwaukee.
The Dow Jones Industrial Average fell 48.91 points, or 0.2 percent, to 24,733.38, the S&P 500 lost 2.78 points, or 0.10 percent, to 2,681.79 and the Nasdaq Composite dropped 8.01 points, or 0.11 percent, to 6,957.35.
MSCI's gauge of stocks across the globe gained 0.02 percent.
In Europe, the premium investors demand for holding Spanish bonds over top-rated German peers fell to its lowest in almost three months as Catalonia held an independence election.
The euro dipped to $1.1817 early in the day, before trimming its losses to trade at $1.1835.
Spanish stocks were among the biggest losers, confirming analyst expectations that any shake-out from the Catalonia vote would be mostly confined to Spain.
Europe's common currency, though, was still up nearly 13 percent so far this year, on track for its best yearly performance in 14 years.
U.S. Treasury yields, which reached a nine-month peak after the American tax vote, pushed slightly higher as investors hung up their hats before Christmas.
The yield curve, while mildly flatter on the day, was on track for its largest weekly steepening since July following the bill's passage, which was seen as hastening the pace of interest rate increases.
Investors appeared to brush off U.S. data on durable goods orders, personal spending, new home sales and consumer sentiment.
Next week, investors will watch for the release of December U.S. consumer confidence survey data. Economists polled by Reuters expect it to decline from its strongest levels since late 2000.
In commodities, oil prices dipped in light trading but remained near their highest levels since 2015 on pledges from OPEC leader Saudi Arabia and non-OPEC producer Russia that any exit from crude output cuts would be gradual.
In cryptocurrencies, bitcoin once again became the most eye-catching mover, this time because of losses. Bitcoin plunged as much as 25 percent on the day at one point to below $12,000, having lost a third of its value since Sunday.
Additional reporting by Ritvik Carvalho in London, Henning Gloystein and Dmitry Zhdannikov; Sruthi Shankar in Bengaluru, and Gertrude Chavez-Dreyfuss and Richard Leong in New York; Editing by Nick Zieminski and James Dalgleish