The Irish defender was a second year apprentice at the Bluebirds and netted one goal in the academy league and that was in the 3-2 defeat against Chelsea on Saturday 24 April but was released last week from the Welsh club.
Last has been recommended by former Stoke City player Terry Conroy who is the FAI's Welfare Officer for young Irish players in Britain.
Conroy told the Sentinel "We know how well Crewe look after their young players. It is a chance for Stephen to show what he can do."
"He's on trial this week and it is a chance for him to show Crewe what he can do."
25-year-old McCarthy netted two goals in the 4-1 reserve win over Burton Albion and the former Kidsgrove Athletic winger impressed by taking his goals well.
McCarthy who has played this season at Warrington Town has put in some impressive displays for the Wire and was linked with a move to Nantiwch Town in 2008 and again in 2009. McCarthy has also played for Alsager Town, Leek Town, Leek CSOB, Biddulph Victoria and also had a loan spell at Leigh RMI when he was at Alsager Town.
McCarthy was sent off in the last away match against for Warrington as they drew against Ossett Town (21 April 2010) but has managed to net 8 goals this season for the Wire.
Newcastle born McCarthy has not long finished university where he is a qualified PE Instructor is a friend of James Bailey.