Valdez pitched six innings for Houston on Saturday after skipping a turn because of a sprained right ankle.
"We can't risk Framber on two or three days' rest for an exhibition game," Baker said in Houston before the Astros played Seattle on Sunday. "I know it's important, but our season is far more important than the All-Star Game. It's an honor to maybe start, but if he's pitching on the route he's in, he'll have three or four opportunities to start in the future. So right now, we got to take care of Framber."
Baker talked with Valdez about the decision.
"He's probably not happy with it," Baker said. "But sometimes you've got to make tough decisions for the player and the team. He's just coming off of an injury. If something happened to him again, I couldn't live with myself."
Romano joined AL replacements that include Seattle center fielder Julio Rodriguez and right-hander George Kirby, Tampa Bay shortstop Wander Franco, Houston outfielder Kyle Tucker, Los Angeles Angels closer Carlos Estevez and Minnesota pitcher Pablo Lopez.
Earlier NL replacements include pitchers Kodai Senga of the New York Mets, Alex Cobb of San Francisco, Craig Kimbrel of Philadelphia, David Bednar of Pittsburgh, Corbin Burnes of Milwaukee along with Arizona infielder Geraldo Perdomo.
Yankees right fielder Aaron Judge, Angels center fielder Mike Trout, Houston outfielder Yordan Alvarez, Tampa Bay left-hander Shane McClanahan, Los Angeles Dodgers left-hander Clayton Kershaw and Chicago Cubs shortstop Dansby Swanson were dropped earlier in the week because of injuries, and Cleveland closer Emmanuel Clase decided to skip the game because of the imminent birth of a child.