The controversial lender rebranded with a new logo on Monday, but it appears to have failed to give the Premier League club enough time to make the changes.
A spokesman for Wonga told the Newcastle Chronicle that due to the lead-time required to make the thousands of replica kits the club had been unable to put the new logo on the shirts. "It was due to the production schedule," he said.
The kit is set to be worn by Newcastle in a game against West Ham on Sunday.
The embarrassment comes just days after the payday lender launched a campaign to improve its poor image and promote the brand as a responsible provider of short-term credit after criticism of its hefty interest rates.
The new ad, which introduces the strapline "credit for the real world", focuses on serving "hard-working people throughout the UK who need access to transparent, flexible and short-term credit products, according to Tara Kneafsey, the UK chief executive of Wonga.
She said new product features and the marketing relaunch were further proof that Wonga is "lending responsibly and putting customer outcomes first". The campaign was created by Fold7.