Washington claimed Krook off outright waivers from the Athletics on Saturday.
Krook struggled during his time with the A's before being DFA'd on Friday, allowing seven earned runs with a 5:4 K:BB over 3.2 innings spanning five appearances. However, the Nationals will look to help him get back on track and in order to utilize him as a lefty option out of the bullpen. To clear room for Krook, Washington designated righty hurler Andre Granillo for assignment and optioned right-hander Zak Kent to Triple-A Rochester.