Tensions boiled over ahead of tomorrow’s FA Cup third-round tie with Scunthorpe after robust tackles were exchanged during training at the Blues’ Cobham base.
Costa took exception to a challenge from Oscar, with the swift intervention of team-mates required to help defuse the situation.
The pair later joked about the incident, but Hiddink suggested the slight Oscar benefits from becoming angry.
“When this guy puts the emotion in, then automatically his level of play rises,” Hiddink said.
Hiddink joked: “We try to punch him every now and then to get him on this level.”
Hiddink downplayed the scale of the confrontation, which came during an “intense” training session.
“It was a pity that our photographer had a day off because he could’ve shot beautiful pictures of two bulls who were chesting a bit after a charge from behind from the smallest bull of the two, which was Oscar,” said Hiddink, who succeeded Jose Mourinho last month.
“He got Diego. Then they stumbled over the ground, stood up as a normal reaction and then chested a bit without any further threat of punching or whatever.
“We came in between, but there was no need to say we had to grab them to avoid them hitting.
“Oscar apologised in front of the group. They looked at each other and then they started laughing. Jokes were made afterwards.”
The Dutchman declined to take sides when asked who would win a hypothetical fight between the pair.
He said: “Diego looks the bigger bull, but Oscar might be a very fast, sneaky bull to make punches.”
Oscar, in particular, has appeared rejuvenated by the managerial change at Chelsea. Hiddink did not wish to compare Oscar’s performances in recent weeks with those under his predecessor, though.
“Players like Oscar, who are blessed by nature in their talent, they know they have to work hard for the benefit of the team,” Hiddink added.
“Maybe they were relying a bit too much on their talent. They are adding now some things. I don’t want to say that it was not (the case) before, but I’m focusing on that because the talent is gifted.”
Another gifted figure is Pep Guardiola. Hiddink tip-toed around the subject of Guardiola declaring his intention to move to the Premier League this summer, with Chelsea among those looking to court the Bayern Munich boss.
“When extra quality can be added, (it is) welcome, I think,” said Hiddink, who ruled out the possibility of becoming permanent boss at Stamford Bridge, no matter how well he does. “We made it very clear that at the end of this then I will stop.”
Chelsea have only one fit striker in Costa, with Radamel Falcao (groin) and Loic Remy (calf) absent. Hiddink did not respond to speculation about Falcao’s loan from Monaco being cut short, only considering the Colombian’s fitness. “I’m worried about his situation,” Hiddink said.
As for new recruits, Hiddink would not be drawn on speculation and also refused to discuss the prospect of Didier Drogba retiring from playing to join him on Chelsea’s coaching staff.
“He’s a big legend for this club, but still under contract with Montreal. We have to respect that,” Hiddink said.
Scunthorpe’s Irish captain Stephen Dawson says they head to west London without fear, however. “I am not scared — it is something I look forward to,” Dawson said.
“You don’t really get the chance to play these kind of players week in, week out.
“Scared doesn’t come into it. It is about 11 of us, the subs, whoever he picks, the whole team going out and really giving our all. It is 11 v 11.
“If they turn up, then, yeah, it’ll be very difficult — we’re under no illusions. We all know we are the underdog. We accept that but we want to go out and do ourselves proud.”