Feldman, who turned 34 on Tuesday, was signed to a one-year, $2.3 million contract on Jan. 26, and he is expected to be Cincinnati's No. 4 starter. He was 7-4 with a 3.97 ERA in 40 games (five starts) with the Astros and Blue Jays this past season.
Diaz, 32, has been with the Reds in each of the past three seasons, but he isn't a lock for a bullpen spot this spring. In 45 games in 2016, he had a 3.14 ERA, retired 30 of 45 first batters faced and allowed six of 19 inherited runners to score.