The phrase "a formidable competitor for" is correct and usable in written English.
It can be used when discussing someone or something that poses a significant challenge or threat to another in a competitive context.
Example: "The new startup has quickly become a formidable competitor for established companies in the tech industry."
Alternatives: "a strong rival to" or "a tough contender against".
A subscription BBC will not just be strong: it will be a formidable competitor for Murdoch.
"It is also clear that they are a formidable competitor for researchers on the market".
"When they grow the business in North America they're going to be a formidable competitor for everyone".
Luqman Arnold, Abbey's chief executive, said the takeover would make the bank a "formidable competitor" for its domestic rivals.
In optical fiber networks, for instance, Alcatel still limps behind Nortel Networks and Lucent, and a combination of Alcatel and Lucent would produce a formidable competitor for Nortel.
Tesco has entered the British video-on-demand market, taking an 80% stake in Blinkbox and creating a formidable competitor for existing services such as Amazon's LoveFilm.
Ill-conceived diversification attempts and heavy borrowing crippled Revco D.S. Inc., once a formidable competitor, which filed for Chapter 11 bankruptcy protection in 1988.
[C2.] Reebok Acquisition Moves Adidas Into Nike's League With its acquisition of Reebok, Adidas will become a formidable competitor to Nike for the first time in more than a decade, with sales of $11 billion and a glittering roster of endorsement contracts that make it close to Nike in size and arguably more powerful in its links to star athletes and teams.
Even after Waterloo, it remained a formidable competitor to Great Britain for power and influence around the world, and it had emerged as a strong rival in the race to colonize Africa and Asia.
It will be a more formidable competitor for tobacconists' shelf space to Altria, Marlboro's manufacturer.
Analysts said the improvements, many of which had originally been expected early this year, would make I.B.M. a more formidable competitor for EMC, the market leader.
