The two players made only a handful of appearances this season before falling out of favour.
Butcher, the former Tottenham Hotspur defender, will not play again in this campaign after breaking a toe in a match with the under-20s, while Erskine has been on loan at former club Partick Thistle since January.
However, Donnelly believes that both can return after the summer and make an impact at Tannadice. "Callum's season is more or less over and it's frustrating for him. He fitted in really well when he joined but it has been a bit stop-start," said the coach.
"He's like Chris Erskine in that he'll come back in the summer. Chris didn't hit the ground running but we know what he's capable of. He'll come back here with the bit between his teeth."