Defender Stephen McManus has returned to parent club Middlesbrough after a three-month loan spell at Bristol City.
The Scotland international made 11 appearances, scoring once for the Championship strugglers.
Meanwhile, the Robins have confirmed that Venezuelan trialist Frank Feltscher has gone back to Zurich, where he plays his football for Swiss club Grasshoppers.
New manager Sean O'Driscoll, officially unveiled as the successor to Derek McInnes on Monday, is expected to make decisions on the future of fellow defenders Mark Wilson and Matthew Bates in the near future.
The duo's contracts at Ashton Gate are set to expire.