A-Rod is a big, important force for the Yankee lineup, and keeping him healthy should be paramount, especially considering his contract. With rosters expanding in only a couple of days, there’s no need to put him on the DL, but he shouldn’t play until he’s 100%. I don’t know how badly his thumb is hurt, but obviously it’s worse than it appeared when it first happened, and, at the risk of sounding terribly obvious, aggravating it would be a bad idea. It sounds like the Yankees are being cautionary here, which is almost certainly the way to go. They can win without Alex, especially considering the playoff picture, but having him at full strength for the playoffs gives them a much better chance.