Sources connected to the "Good Morning America" host and NFL Hall of Famer tell us he is currently quarantining ... which is why he's been absent from 'GMA' all week.

Football fans also noticed he only appeared remotely for his other gig on "FOX NFL Sunday" during the NFC Championship -- that's because Michael was already taking precautions.

We're told he found out on Saturday he'd been exposed at some point last week, and immediately started quarantining. Our sources say he's planning to appear on 'GMA' Thursday, remotely, to discuss his diagnosis. He's not currently experiencing any severe symptoms.

There's also this ... we've learned Strahan's daughters came into contact with him AFTER he'd been exposed -- so they're getting tested. So is their mother, Jean, with whom they live most of the time. We're told they haven't gotten their results yet.

It's unclear how much he'll be working for now. We've seen other anchors work from home while quarantining -- CNN's Chris Cuomo comes to mind.