Castro was diagnosed with a Grade 1 right hamstring strain. Ellsbury on the other hand has a right knee bruise and is day-to-day.
With the teams playoff hopes taking a big hit this weekend by losing three of the first four games in Boston, losing Ellsbury and Castro for a long stretch of time will almost certainly hinder their chances. Castro has been one of the more productive player in the lineup for the Bombers this season.
Good news is that both players will get treated again Monday and rejoin the team in Tampa Bay Tuesday.