Rotherham United rocked by double blow as two centre-halves are sidelined
Tilt has a hamstring injury and is out of action until October while manager Paul Warne says MacDonald will be absent because of an unspecified "little problem".
The double setback will force the club into the transfer market because they now have to just two fit senior central defenders available to them: Michael Ihiekwe and skipper Richard Wood.
"Curtis severely pulled his hamstring while he was away," said Warne whose squad returned to Roundwood for pre-season training yesterday. "That's a 12-week injury.
"Angus isn't fit either. There's a little problem with him. He's going to miss the start of the season also.
"We're down to two centre-halves so that is something we're going to have to address. We need defensive cover."
MacDonald played a big part for Rotherham in the Championship last season while Tilt spent the year on loan at League One Wigan Athletic who are keen to sign him on a permanent basis.