Richards is already on the 40-man roster and is lined up to pitch that day, and Mills -- sent down in order to create roster space for Saturday starter Jerome Williams -- can't be brought back up to the Majors if someone isn't placed on the disabled list.
Richards has struggled mightily of late, giving up 12 runs over his last two outings for the Angels, then getting charged with eight earned runs in 3 1/3 innings in his first start back with Salt Lake on Thursday.
"A young pitcher that's still developing, with a power arm, some of the things he's going through are not uncommon," Scioscia said. "When he makes his pitches in good zones, his stuff plays big time in the Major Leagues. That's where hopefully he's going to be as he continues to progress."