As Celtic prepare to open up their Champions League campaign against Slovan Bratislava, UEFA begins the build-up to the big game with an interview with Callum McGregor. The Celtic captain is set to embark on another group-stage adventure against Europe’s elite clubs and whilst he has enjoyed a successful career at Celtic Park, it wasn’t always plain sailing for McGregor in Paradise. The 31-year-old midfielder is an experienced campaigner for Celtic on both the domestic and European stages but there was a ‘turning point’ at Celtic that McGregor felt was pivotal in his career at Parkhead. McGreg…