Nicholas (knee) will begin a rehab assignment at Triple-A Round Rock on Monday, Stefan Stevenson of the Fort Worth Star-Telegram reports.
Nicholas has seemingly recovered from the knee surgery he required in early March, but after being sidelined for much of spring training, he may need multiple weeks worth of games to get his conditioning in order. Once he's activated from the disabled list, Nicholas will likely remain with Round Rock, as Jonathan Lucroy and Robinson Chirinos are the clear top two catchers in the organization.