"We're trying to figure out how we're going to set up our rotation through the course of the weekend," Amaro said.
Lee is 10-4 with a 3.05 ERA and 131 strikeouts in 20 starts this season. Raul Valdes got the nod in his place against the Tigers last weekend and allowed nine runs in 3 2/3 innings.
In other injury news, Amaro said left fielder Domonic Brown is "probably a week away" from returning. Amaro added Brown could make a rehab appearance or two before rejoining the Phillies.
Brown sustained concussion-like symptoms after he landed hard while diving for a fly ball last Tuesday against the Cardinals. Amaro said Brown passed a concussion test Wednesday and will have another one Thursday. The 24-year-old has a team-best 24 homers and 69 RBIs this season.
Stephen Pianovich is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.