I could understand that if he'd given a poor performance or if the film had been derided, though I know that wouldn't necessarily be know when the film was released, who were the other two?
Found an interview with Everett on the web where it says:
Since then, Everett briefly appeared, unbilled, as Christopher Marlowe in Shakespeare in Love (and although he considers it, with Rushmore, one of last year's two best films, he also insists, "Actually, I was very, very bad in it ‑ I was a bundle of f‑‑‑ing hideous nerves').