Pulisic's introduction at half-time sparked a second-half comeback from Dortmund to beat Liverpool 3-1 in the International Champions Cup fixture as the 19-year-old, playing in his home country, netted a penalty, coolly finished off a counter-attack for an 89th-minute victor and then set up Jacob Bruun Larsen's late strike.
"Stay strong Karius, it has happened to the best of players", he said.
The arrival of the Brazil No. 1 from Roma - in what is the biggest-ever transfer fee for a goalkeeper - means Karius will no longer be considered first-choice at Anfield.
Karius himself had posted a message via an Instagram story after the match which read: "To those who take joy in seeing other people fail or suffer, I feel for you".
The Reds have been linked with a move to bring the talented 19-year-old to Anfield in recent months as Klopp looks to add to his attacking options at the Merseyside club.
"If - at one point - he will join us, I don't know".
"I do not know that, I can not say what I'm doing right now, there's still some time left [in the transfer window]".
"It's not the same injury".
"We will see, but we can not say any more about it now".
"I like him, it's not that that could be the problem, but we respect contracts still and there's no market I know about at the moment".
His dodgy display was subsequently blamed on concussion.
Matip was favourite to partner Virgil van Dijk on the opening day of Liverpool's Premier League season against West Ham but any kind of injury will threaten his chances of even making the squad with just 20 days until the start of the new campaign.
For Dortmund, Pulisic somehow found his side a way back into the game, winning a penalty midway through the second half having worked nicely in the box.
After Pulisic cut in from the left and fired a shot at goal, Karius managed to palm it away.
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