The authors question if a sports celebrity endorsing multiple products actually is strengthening their own brand at the expense of the products endorsement from outside their field of sport. The authors conclude from their first tests of the hypotheses in this area that when a celebrity sports endorser is paired with a product from their sport, likability and trust of the endorser increase more significantly than top-of-mind awareness of the brand itself (Koernig, Boyd, 34). Second, no differences existed between athletes and on-athletes when endorsing a non-sport brand. The anonymous endorser portrayed as an athlete is in fact more effective promoting a sports brand and aiding its top-of-mind and unaided awareness according to the results of the two studies (Koernig, Boyd, 35). Moat significant from this study is the finding...

This was ascertained by comparing the results of the two studies, and finding that the anonymous athlete, when defined by implied athletic achievement and not by fame, actually contributed the most to brand awareness and interest over celebrity endorsers. The greater the fame of endorsers, the more non-brand endorsements first benefits the celebrities' image as trustworthy (Koernig, Boyd, 35). For best results, pairing an anonymous athlete with a sports brand delivers the greatest benefit to brand identity.
Reference

Koernig, S., and T. Boyd. "To Catch a Tiger or Let Him Go: The Match-up Effect and Athlete Endorsers for Sport and Non-Sport Brands. "…