It is simply not possible for market participants to make long-term gains from current U.S. stock prices, an investment manager told CNBC on Tuesday.

Wall Street is widely considered to be in a bull market, with the S&P 500 having quadrupled in value since March 2009. Last week, the index's current run-up in stock valuations turned 3,453 days old — making it the longest streak in history, according to some investors' definition.

But, after nine years and five months, a number of investors feel it is now just a matter of time before such a run comes to an end.

"It can't get better than this, absolutely can't get better than this, but don't worry it will carry on because Wall Street says so … It is nonsense, utter nonsense," Peter Toogood, chief investment officer at financial advisory firm Embark Group, told CNBC's "Squawk Box Europe."

"The valuation metric is a matter of fact, not opinion, OK? You don't buy here, you will not make long-term money out of investing today from these levels. Period."