Zimmermann threw a bullpen session Tuesday, Dan Kolko of MASNsports.com reports. Zimmermann typically throws his bullpen two days before his next outing, so Tuesday's session would seem to line him up to start a potential Game 5 of the NLDS on Thursday. Nothing's set in stone, however, and the Nats may very well go with Stephen Strasburg on five days' rest, if they do indeed manage to extend the series with a win Tuesday.