Marshalls tags are attached to merchandise in a store in Methuen, Mass. On Friday, Oct. 13, 2017, the Commerce Department releases U.S. retail sales data for SeptemberRetail Sales, Methuen, USA - 16 May 2017

TJX Cos Inc. has become used to winning, grabbing market share and picking up momentum as it became the second-largest apparel retailer in the U.S., right behind Walmart Stores Inc.

But now the off-price giant is coming up against a foe that might simply prove to be too much — the law of large numbers.

It’s hard to call just when a company becomes too big to maintain its growth rate — Walmart Stores Inc. went from big to huge to gigantic to mammoth before it started to see growth slow. But Wells Fargo analyst Ike Boruchow said recent missteps from TJX suggest the time could be drawing near.

Boruchow downgraded TJX to market perform from outperform, citing in particular the size of the company’s Marmaxx division, which includes T.J. Maxx and Marshalls. The company’s stock took a hit from the downgrade, but bounced back quickly, and managed to post a gain of 0.9 percent to $76.46 for the first week of the year.

The downgrade was controversial given TJX’s position as the apparel powerhouse in the minds of many investors. And while the downgrade’s immediate impact on the stock might have passed, consider the change of opinion something of a warning sign for what has been the most successful brick-and-mortar apparel player in recent years.

“You could have made the argument they were too big a year ago or two years ago if you wanted to,” Boruchow told WWD. “I think it’s easier to make the argument now because their business is starting to slow down.”

Unlike Walmart, with an offering that stretches from food to electronics to apparel, TJX is highly concentrated in fashion, and then the home business. And TJX, with sales of more than $33 billion, has grown to a size where it can no longer rely on the traditional off-price model of buying excess goods from full-price sellers.

Boruchow said it’s easier for smaller off-pricers, such as Burlington Stores Inc., which has total sales of $5.5 billion, to be “flexible” and “rely more on closeouts and more brands, and the way you buy and build the model, it’s easier.”

“When you’re Marmaxx, you have to kind of start sourcing the business more like a department store because you can’t wait for closeouts. Last quarter, they called out a fashion miss as part of their negative comp. [Comparable-store sales fell 1 percent at Marmass in the third quarter]. Is this Macy’s?”

According to Boruchow’s tally, it’s actually bigger than Macy’s.

The analyst pegged the U.S. retail market at $353 billion. Walmart takes the biggest chunk of that, with apparel sales of $24.7 billion, ahead of Marmaxx at $18.1 billion, Macy’s at $16.8 billion and Amazon.com at $15.6 billion.

Boruchow said he’s been a bull on TJX for two-and-a-half years and still sees the company as a player, but that the outlook has changed.

The fashion business has also changed.

The analyst pointed out that inventory across apparel is the cleanest it has been in five years and that brands that warmed to selling to off-pricers after the recession are growing more reluctant and starting to pull back.

“A rationalized inventory environment combined with vendors pulling back off off-price distribution will make it difficult for the world’s largest off-pricer to generate growth rates similar to years past in our view,” Boruchow told clients in a note.

He pointed out that Marmaxx needs to generate $250 million more in sales to add a single point to its comp sales.

“Marmaxx needs to create a small apparel company each year just to grow comps by one point (Canada Goose was around $250 million around 18 months ago, for example),” he said.

TJX has done just that for a long time, but just how long it will be able to keep it up is an open question. And it’s a question that Wall Street’s starting to ask.