The centre-back was lucky not to be penalised five minutes before the end of the period when he brought down Dwight Gayle with a clumsy challenge on the edge of the box.
Despite the penalty calls from Newcastle head coach Rafael Benitez and their home fans, the referee let the game continue and the sides went in 0-0 at the break.
"For me it's a penalty. He doesn't get the ball, he gets the player and it's inside the box," ex-Liverpool star and manager Souness said. "What more do you need to know?"
Henry added: "It was a penalty."
While Newcastle fans and pundits may criticise the referee for the decision, United fans have turned on Smalling for a horrendous display and what could have been a costly mistake.
How does Smalling still play for us? Just saw the penalty incident on Gayle. Why's he even challenging him there? Senseless.— Doc (@Doc_Joshi) February 11, 2018
Blatant penalty for Newcastle that. Smalling gets nothing of the ball and the ref is stood in the perfect position to see it. Gives nothing. Even @GNev2 agrees it's an obvious foul.— Joel Rabinowitz (@joel_archie) February 11, 2018
Time for Lindelöf to start playing. Can't deal with watching Jones and Smalling attempt to build from the back.— Jordan Clarke (@FourFourJordan) February 11, 2018
That's a penalty for Newcastle. Smalling comes barreling in like the idiot he is & gets lucky that it's not given. Shithouse modern defender.— Adam Joseph (@AdamJosephSport) February 11, 2018
Martial left, Sanchez middle, Jesse right and Smalling with the fishes— Alaska Thunderfuck (@NickiiDupre) February 11, 2018
I keep wondering how many plates Smalling broke as a kid..... That guy is clumsy af #NEWMUN— MILLY ROCK FC (@OVERDOZiE) February 11, 2018
Smalling is comfortably the worst CB I've watched. Utterly horrendous.— Ben Smith (@bensmith130) February 11, 2018