NEW YORK (TheStreet) –- Staples (SPLS) , the largest U.S. seller of office products is confronting declining North-American sales just as shareholders are hoping for a big payday from its pending merger with rival Office Depot (ODP) - Get Report.

The company's second largest business unit is not generating the type of profits that it could. The merger is also unlikely to win regulatory approval any time soon, although there are also no guarantees the merged company will be better off than the separate parts. 

That's at least partly because the money both companies may save through the merger won't withstand pressure from online retailers, including Amazon (AMZN) - Get Report, who do not face the same encumbrances from real estate costs. Investors should focus on growth, not on how much this merger may gain by merely rearranging store locations.

To be sure, to the extent the merger can drive higher revenue, there will be incremental benefits to shareholders. As of Friday's fourth-quarter financial results, revenue at the company's North-American Commercial unit climbed 5% above last year to $2.05 billion. That accounted for 36% of Staples' fourth-quarter revenue of $5.7 billion.

Likewise, full-year North-American Commercial revenue rose 3% above last year to $8.3 billion. That accounted for 37% of total 2014 revenue of $22.5 billion.

However, in both cases, Staples didn't earn the kind of profits on those sales that maximize shareholder returns.

Although fourth-quarter North-American Commercial revenue climbed 5%, operating income rate declined 1.4 percentage points to 7.1%, resulting in an operating profit of $145 million. That represents a 13% decline from last year's mark of $167 million. On a full-year basis, it was the same thing.

Full-year operating income for North-American Commercial revenue was $571 million, down more than 5% from last year's mark of $604 million. The decline was due to a 60 basis-point decline in full-year operating income rate, reaching 6.9%.

This means Staples, while making investments to grow its second-largest business, is not getting the return it needs to justify its expenses. A commercial monopoly in North America is what investors were hoping for with the Office Depot tie-up. The expected benefits included not only larger business contracts, but also better government and commercial deals.

Investors must now ask if Staples can make money from that segment even if these deals occur.

Complicating matters, its largest segment -- North American Stores and Online -- continues to suffer. Staples reported fourth-quarter revenue of $2.7 billion, which declined 7% from last year's mark of $2.9 billion.

The lone bright spot? -- Staples.com, the company's online business, which grew fourth-quarter revenue at 9%. The Online segment of the company's North American Stores and Online unit generates about $2.1 billion. 

Nonetheless, sales growth alone means nothing without profits. Investors don't know how much it costs to operate. Online is being lumped in with "North American Stores and Online (units)." 

Overall, Staples is suffering weak profits from two segments that account for 83% of its sales (North American Stores and Online and North-American Commercial). With plans to close 225 stores this year if its merger with Office Depot is approved, profits may decline further. Closing stores cost money.

There will be expenses tied to laying off workers and terminating leases. The stores Staples does keep will have a tough time making money, given the onslaught of online shopping. Staples' own online business is evidence of that. 

Perhaps online offers Staples its biggest hope. 

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.