Betts didn't accompany the Red Sox to New York, but will be in Detroit.
"He had a good day Sunday," said Red Sox manager John Farrell. "Another good day [Monday] with the increase of physical activity. There's no reproducing of the concussion symptoms right now."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.