The Rays designated Armstrong for assignment Sunday, Marc Topkin of the Tampa Bay Times reports.
The righty gets demoted after allowing four earned runs total in his last two appearances. Armstrong's 4.50 ERA in 16 innings since joining the Rays is respectable, and the Rays' frequent bullpen shuffling suggests he could find himself back with the club in the near future. That is, unless he gets claimed off waivers. Nick Anderson (elbow) was activated from the 60-day injured list to fill Armstrong's 40-man roster spot.