In 1996–97 he moved into the professional ranks with Coventry. It was Coventry's most successful period of the modern era, coming within touching distance of the Premiership. Along the way, with Grewcock an ever-present, they beat a Newcastle Falcons side featuring 15 internationals by 19-18 at Coundon Road. They eventually finished third to Newcastle and champions Richmond, and lost a promotion play-off against London Irish despite taking a narrow first leg advantage to Sunbury. Despite their second-tier status, both Grewcock and team mate Rob Hardwick were capped by England in this era.