The phrase "a former competitor" is correct and usable in written English.
You can use it to refer to someone or something that previously competed against another in a specific context, such as business or sports.
Example: "After years of rivalry, the two companies decided to collaborate, putting aside their differences as former competitors."
Alternatives: "an ex-competitor" or "a past rival."
Now a former competitor is consolidating control over Novokuznetsk Aluminum.
Atle Skaardal, the women's race director and a former competitor from Norway, defended the decision to cancel the race.
It is now controlled by a former competitor, one that has cultivated a relationship with the governor.
It later changed its name to Royal Engraving, and merged with a former competitor, Palographia, about seven years ago, said Larry Paladino, who now co-owns the firm.
"It was a big story all over the badminton world that he has come back from this illness," said Koukal's coach, Dicky Palyama, a former competitor from Holland.
The panel featured a former competitor, a YouTube cooking sensation known as the Vegan Black Metal Chef, and a representative from the Keep a Breast Foundation, the breast cancer charity to which the evening's proceeds were dedicated.
Sacby.com was previously owned by feminine online shopping site, 24h00.com, a struggling former competitor of Vente-privée.
She lives with Emé, a Frenchman and former competitor on the TV show "Iron Chef America: The Series," and daughter, Gisele.
But Video Busters is a rare thing purely by existing: in the middle of suburbia, it remains open as nearly every other video store — including its former competitor, a Blockbuster just around the corner — has gone out of business.
Meanwhile, CMGI, a one-time incubator and former competitor of Safeguard has changed its tune moving from the incubator space to providing supply-chain management.
Angry but undeterred, Hostetler moved into cheap housing nearby provided by a former Norwegian competitor and kept showing up at the center every day to train.
