Doolittle announced his retirement from baseball Friday.

Nationals manager Dave Martinez announced Friday that Doolittle has been diagnosed with a patellar tendon strain in his right knee, Bobby Blanco of MASNSports.com reports.

Doolittle (elbow) was placed on the 7-day injured list Wednesday at Triple-A Rochester, Bobby Blanco of MASNSports.com reports.

Doolittle (elbow) has been transferred from Double-A Harrisburg to Triple-A Rochester, Jesse Dougherty of The Washington Post reports.

Doolittle (elbow) was activated Tuesday off the minor-league injured list, Bobby Blanco of MASNSports.com reports.

Doolittle (elbow) is scheduled to pitch again Friday at Low-A Fredericksburg, Mark Zuckerman of MASNSports.com reports.

Doolittle (elbow) had his rehab assignment transferred Tuesday from High-A Wilmington to Low-A Fredericksburg, Mark Zuckerman of MASNSports.com reports.

Doolittle (elbow) began a rehab assignment at High-A Wilmington on Saturday and struck out two while allowing one hit in a scoreless inning of relief.

Doolittle (elbow) has begun back-to-back mound sessions at the Nationals' spring training complex in Florida, Mark Zuckerman of MASNSports.com reports.

Doolittle (elbow) threw live batting practice Tuesday at the Nationals' spring training complex, Jessica Camerato of MLB.com reports.