The 16-year-old, son of former Mapgies midfielder Lee Clark, was also on the bench for the UEFA Youth League opener against AC Milan, having settled in quickly at Kirkby.
Klopp has already taken a look at Clark in first-team training, as part of a young group padding out the numbers during the international break.
It was Klopp who, along with academy director Alex Inglethorpe, helped convince Clark to join Liverpool ahead of Man United, Man City, Tottenham and Leeds, with visits to Kirkby and Anfield helping him make the decision.
Interestingly, O’Neill notes how United’s signing of Ethan Ennis from Liverpool earlier in the summer financed the deal.
Ennis swapped Merseyside for Manchester in a deal worth £750,000 rising to £1.5 million, plus a sell-on clause, with “almost identical” terms agreed with Newcastle by assistant sporting director Julian Ward.
It is a sizeable fee for a player who, unlike Gordon at Derby, did not make his first-team debut for Newcastle – nor, despite Steve Bruce’s protests after the deal’s completion, was he close to a breakthrough.
Along with sessions under Klopp and Lijnders, Clark has also worked with both Robbie Fowler and Steve McManaman, part-time coaches at Kirkby, since his arrival.
Liverpool appear to have taken a shift in their approach to youth recruitment in recent years, with Inglethorpe presiding in a quality-over-quantity stance.
A focus on homegrown talent is encouraged, with Clark the latest example, joining an U18s side that also includes the likes of James Balagizi, Luca Stephenson and Oakley Cannonier.