Bostock lay motionless near the east stand of BMO Field, then pounded the turf in frustration.
He was ignored. The practice continued as he didn't exist.
The 21-year-old Englishman finally got the message. He got up, flexed a knee and then resumed practice.
With almost the whole squad healthy, competition for places is fierce. And it showed Tuesday as players put their body on the line.
Defender Richard Eckersley emerged with a bloody nose while midfielder Terry Dunfield made a stop on the sidelines to bandage a bloody knee before bounding back onto the field.
"I don't like to see blood on the players," manager Ryan Nelsen said with a smile, "but what I do like to see is it's competitive and guys are getting stuck in. And some of those things happen.
"But what I like is the reaction. You don't make it into a farce. A bit of blood never hurts anybody, but we carry on and we play and we're professional. We keep working, we don't have any excuses. It doesn't turn into a fight or anything like that.
"We all have emotional control, if you know what I mean, and we get about our business."
Nelsen didn't name names but, for those listening, pointing the finger at Bostock wasn't exactly coming up with Colonel Mustard in the library with a candlestick.
"We don't like very many divas," Nelsen continued.
While Toronto trained Tuesday, their next opponent — the defending MLS champion Los Angeles Galaxy — was feted at the White House.
After a bye week, Toronto (1-2-0) hosts the Galaxy (2-0-1) on Saturday.
Less than two months since taking on the job full-time, Nelsen has managed to instill in Toronto FC an ethos that performance pays off in minutes on the field.
It's the underpinning of every successful franchise and one that is hardly a secret. But lack of talent — and to some extent injuries — has often handcuffed Toronto FC.
Former manager Paul Mariner was often hard-pressed to fill his bench after taking over for Aron Winter last season.
TFC's lack of depth was illustrated by the bench for the July 21 game against visiting Colorado — Toronto's last win of the season as the club lurched through a 14-game winless streak the rest of the campaign.
The Toronto substitutes were goalie Quillan Roberts (17), defenders Aaron Maund (21) and Dicoy Williams (25), midfielders Oscar Cordon and Matt Stinson (both 19) and forwards Keith Makubuya (19) and Andrew Wiedeman (22).
Only Roberts and Wiedeman remain with the squad and Roberts is currently away with the Academy team.
Nelsen, president Kevin Payne and chief scout Pat Onstad have not been shy about personnel changes. There are doubtless a few more to come but the quality of the squad and its attitude have already definitely been upgraded.
On Tuesday, Welsh striker Robert Earnshaw showed off a shimmy that would have done "Dancing with the Stars" proud as he left a goalie rooted to the spot.
Bostock left defenders reeling with a shake of the hips and a few stepovers. English midfielder Hogan Ephraim also brought it, finishing in style. And Wiedeman hammered a long-range rocket off the crossbar.
For veteran defender Danny Califf, a 10-year MLS man who is new to Toronto FC this season, Tuesday's training session told a tale.
"That's one of the things that the coaching staff has brought in — a real sense of competition, a real sense that the standard needs to be set every day at training," said Califf. "You can't take trainings off. And when that standard is set, then the intensity ramps up.
"Each one of us here is a competitor, I think you can't make it here without being a competitor. And so when you're in that situation, the emotions are going to get high, things are going to get intense. And I think that brings out the best in each one of us."
With defenders Darren O'Dea (Ireland) and Ashtone Morgan and midfielder Kyle Bekker (both Canada) still not back from international duty, Nelsen deployed Eckersley at left fullback and Darel Russell on the right in training Tuesday.
Attacking midfielder Luis Silva, recovered from a hamstring problem, impressed with some deft passing, as did veteran midfielder Julio Cesar, who is returning from a calf strain.
It makes for a pleasant selection headache for Nelsen.
"I think the guys who have played the first three games, there's not very many of them that haven't done well, have they?" he asked. "They've all really put in some good work. We could be one win and two draws ...
"The guys know that there's competition," he added. "For everybody ... You have to be starting for Toronto by merit. Not by reputation, not by anything."
Character is crucial to Nelsen, who clearly understands how much the under-performing franchise owes its fans.
His goal is to build a winner, but he knows that will take time. In the meantime, he is working on constructing a prickly team that is no fun to play against.
Nelsen continues to pay tribute to the more than 4,000 TFC fans that travelled to Montreal to see the March 16 game against the Impact, saying that there aren't many places in the world that would see that number travel that distance.
"The guys are really indebted. There hasn't been much success here. Ever. And yet they still passionately support the team and they turn up and they're desperate for the team to do well.
"And that resonates with not just the players but myself, the coaching staff, everybody that works for Toronto FC."