Happ went 1-for-4 with a three-run home run in Tuesday's 5-4 loss to the Diamondbacks.
Webb (6-4) allowed two runs on one hit and one walk without recording a strikeout in one inning, taking the loss and a blown save in Tuesday's 5-4 loss to the Diamondbacks.
Holmes allowed two hits and two walks while striking out five over seven scoreless innings in a no-decision versus the Diamondbacks on Tuesday.
The Nationals are expected to recall Perales from Triple-A Rochester on Wednesday, Kyle Williams of TheBanner.com reports.
The Nationals optioned Bird to Triple-A Rochester following Tuesday's game against the Rockies.
Waldron will serve as the opening pitcher in Wednesday's game against Colorado, Mark Zuckerman of NatsJournal.com reports.
Kelly is absent from the lineup for Tuesday's game against the Diamondbacks.
Wynns and the Cubs agreed on a minor-league contract Tuesday.
Ruiz is absent from the lineup for Tuesday's contest versus the Rockies.
Chaparro is absent from the lineup for Tuesday's contest against the Rockies.
