Petit was critical of the German defender and also said he has reservations about Arsenal boss Unai Emery.
He told RMC (h/t ESPN FC): "I was surprised to see Mustafi picked for that game, because he is after all the king of blunders. Even though it shouldn't have been a penalty because there was an offside, it's Mustafi who gives away the penalty again."
He added: "Emery steers the ship well, but there are certain things in his management style that concern me. I hope I am wrong."
With Arsenal leading at Wembley Stadium thanks to Aaron Ramsey's early goal, Mustafi brought down Harry Kane in the penalty area to hand Spurs a spot-kick, which Kane subsequently dispatched in the 74th minute.
Football.London's Charles Watts was frustrated with the defender's slip-up:
Charles Watts @charles_watts
Taking the offside out of the equation, the Spurs penalty sums Mustafi up in a nutshell. Played out of position and coped well, took very few risks all day and a did a good job for the team. Then an utterly brainless moment ruins it all. Just don't get what goes through his head.
Watts' colleague James Benge was also critical of Mustafi, but he liked Emery's approach to the match:
Though Bernd Leno was forced to make a superb double-save to deny Christian Eriksen and Moussa Sissoko in the first half, Arsenal were perhaps the better side for much of the contest.
Had Alexandre Lacazette not been uncharacteristically wasteful—he was guilty of missing a golden opportunity from eight yards—and his replacement Pierre-Emerick Aubameyang scored his injury-time penalty, it could have been a different story for the Gunners.
Arsenal blogger James McNicholas praised Emery after the match:
The Gunners may only be one place higher than they were at this stage last season under Arsene Wenger—and still outside the top four in fifth—but they're 12 points better off.
There's still a long way to go until Arsenal can vie for the title again, and they're still waiting for their first away win at a top-six rival since January 2015.
However, as Emery looks to reverse years of decline under his predecessor in a season of transition, it has been a promising start for the Spaniard.
As for Mustafi, he's 26 now and still yet to grow out of making costly errors, so Arsenal might be best served by finding a more reliable replacement for him as they look to push up the table in the coming years.