Not long after Happ was injured Tuesday night, McCarthy's wife, Amanda, tweeted: "Thoughts go out to Happ and his family. Such a scary moment."
Major league general managers discussed the issue during their meetings in November and MLB presented several ideas at baseball's winter meetings only weeks later.
MLB staff have said a cap liner with Kevlar, the high-impact material used by military, law enforcement and NFL players for body armor, is among the ideas under consideration.
The liners, weighing perhaps five ounces or less, would go under a pitcher's cap and help protect against line drives that often travel over 100 mph.
MLB could implement the safety change in the minor leagues, as it did a few seasons ago with batting helmets, but would require the approval of the players' union to make big leaguers wear them.
Brad Lincoln replaced Happ, who gave up four runs — all in the second — and five hits in 1 1-3 innings.
Several players around the majors tweeted their thoughts and prayers for Happ and his family.
"Take for granted how fast this sport can be, Especially for players that close. No reaction time!" Dodgers infielder Jerry Hairston Jr. wrote.
Happ began spring training without a spot in Toronto's projected rotation. He earned a starting role when the Blue Jays left struggling Ricky Romero behind in Florida to work on mechanics when the season began.
Happ was obtained by Toronto in a trade with Houston last July 20. He was placed on the disabled list Sept. 7 and missed the rest of the season due to a broken right foot.
The Blue Jays grabbed a 6-4 lead in the ninth on Maicer Itzuris' solo homer and an RBI double by Melky Cabrera off Joel Peralta (0-2). Toronto, which trailed by three early on, tied it at 4 in the eighth on Jose Bautista's RBI double.