The stock market is in for a few surprises this week, including one "big wild card," Art Cashin told CNBC on Monday.
"All eyes this week will be on Thursday," UBS' director of floor operations at the New York Stock Exchange said on "Squawk on the Street." "You've got the British election, you've got the ECB, and you've got Comey's testimony. ... That would be an absolutely big wild card."
Former FBI Director James Comey will appear before a Senate panel Thursday in his first public testimony since President Donald Trump fired him. He'll likely be asked about his reported conversations with Trump on ex-national security advisor Michael Flynn.
The Dow shed more than 300 points in mid-May after a report by The New York Times said Comey put together a memo outlining a conversation in which Trump allegedly asked him to halt an investigation into Flynn.
The panel meets on the same day as Britain's general election, which British pollsters predict Prime Minister Theresa May will win, and the European Central Bank's decision on rates.
U.S. equities were mixed on Monday after record highs last week. On Friday, the Dow's record close was its 17th of 2017. The S&P 500 posted its 22nd and the Nasdaq set its 37th of the year.
Cashin said the market is "suspectable to air pockets and surprises."
"I would be very careful with Thursday. A lot of potential built into that day," he warned.
—CNBC's Peter Schacknow contributed to this report.