The Magpies lost their second successive Premier League game, as they went down 1-0 to West Brom at The Hawthorns.
Darren Fletcher’s goal in the 78th minute proved to be the difference between the two sides.
Newcastle goalkeeper Karl Darlow was at fault for the goal, as he allowed Fletcher’s header to squeeze past him.
It was the former Nottingham Forest player’s Premier League debut, having been drafted into the team as a late replacement for Rob Elliot.
Former Newcastle goalkeeper Harper has played down Darlow’s mistake on Twitter, claiming that it is not the fault of the 2014 summer signing from Forest that Steve McClaren’s side lost.
The 40-year-old has also underlined the importance of Newcastle’s next two Premier League games, which are against Arsenal away and Manchester United at home.
Newcastle are third from bottom in the Premier League table at the moment with 17 points from 19 matches.
It is only going to get tougher for the Magpies, as winning against Arsenal at the Emirates Stadium and against United at St. James’ Park will not be easy.
Given that way the Gunners are playing at the moment, Steve McClaren’s side are unlikely to get anything from the match in North London on January 2.
A point against United at home on January 12 is possible, but the Newcastle players will have to be at the top of their game for that.