Castro (knee) is expected to toss a bullpen session Tuesday, Roch Kubatko of MASN Sports reports.
Castro was scratched ahead of his scheduled Grapefruit League start Sunday due to tendinitis in both knees. He received treatment on the knees, as well as his lower back, and stated that he wasn't too concerned about either ailment. If all goes well with Tuesday's bullpen, Castro will likely take the mound in a spring game next week.