The following season (2004–05) saw Wallace play more games for Celtic, including three appearances as a substitute in the Champions League. However he made little impact in either his league or European appearances. Wallace did however score a hat-trick in an 8–1 rout of Falkirk in a Scottish League Cup tie in September 2004. That performance earned him public praise from his manager, Martin O'Neill. Alan Thompson also said that Wallace was likely to succeed him in the future at left midfield.