Horwood, 21 has moved to Gretna FC on loan until January last Friday but wasn't included in the team that lost 4-0 at Glasgow Rangers a day later.
Meanwhile Robertson joined Dundee United last Monday on loan, also until January and repaid his new club with a winning goal in the CIS Insurance League Cup.
The Terrors won 2-1 at Tannerdice Park on Wednesday night against Ross County; and with the score locked at 1-1 Jordan Robertson came up in the 88th minute to secure the win for United.