Equity strategist Andrew Garthwaite warned investors could be in for a "difficult phase" and end the year flat.
The S & P 500 and Dow Jones Industrial Average reached record highs last week, with the former breaking above 5,100 for the first time on an intraday basis.
The S & P 500 and Nasdaq are both up more than 6% this year, and the Dow has climbed 3.8%.
Garthwaite admitted his downbeat outlook could be wrong, as productivity gains from AI could lead to a 15% to 20% advance for the S & P 500.
Market breadth is also typically better when stocks reach new highs, according to Garthwaite.
Persons:
Andrew Garthwaite, Dow, Garthwaite
Organizations:
UBS, Equity, PPI, Dow Jones, Nasdaq, Nvidia
Locations:
Japan