Interim boss Guus Hiddink revealed on Friday that the striker suffered the injury in a training ground collision with an unnamed academy player, who was training with the first-team squad.
It later emerged Canada-born defender Fikayo Tomori was the player involved.
"Yesterday in training Diego got in a duel, got his nose broken," Hiddink said.
"It was not this tough duel, but he put his nose on the back of the head and he was very unlucky."
Costa is poised to join fullback Cesar Azpilicueta in wearing a protective face mask in this weekend's Premier League clash with the Magpies. Azpilicueta is recovering from a fractured cheekbone.
The Spain striker's mask was due to be fitted on Friday before a light training session to test his readiness to play.
Hiddink added: "Today is the day they put on a mask. We are a team with a lot of masks. A Zorro team.
"I hope. I'm not sure, but I think he will be available."
Nemanja Matic and Gary Cahill have also worn protective masks this season, while Cesc Fabregas is among those to have worn masks in recent seasons.
Costa has scored seven times in nine games for Chelsea, including to earn a 1-1 Premier League draw at home to Manchester United last weekend.
The blow was a reminder of Chelsea's reliance on Costa, with Loic Remy (calf) out in recent weeks and Radamel Falcao (thigh) absent since October.
Hiddink, whose initial reaction to Costa's blow was a worried groan, added: "When things happen, we go ahead with the people available. And with confidence."
Chelsea's defensive options have been reduced, too, after Kurt Zouma suffered a season-ending knee injury against United, meaning a likely return to the starting XI for Cahill against Newcastle.
Hiddink would not be drawn on whether the blow for Zouma might have implications for captain John Terry.
The 35-year-old last month announced Chelsea would not be renewing his contract, but the club insisted the possibility remained the captain would be offered an extension.
Hiddink added: "That's something to be answered by the management and the board and the directors of the club.
"The door was open and is open. We'll see what will happen with this."
The subject of a permanent successor to Jose Mourinho, whom Hiddink replaced on a caretaker basis in December, was also something the Dutchman did not wish to broach.
"It's up to the board and to the management," Hiddink added.
Matt Miazga, who signed from New York Red Bulls last month, moves up the defensive order in Zouma's absence, but is unlikely to be included just yet, while Jake Clarke-Salter has been training with the first team of late.
Alexandre Pato is still short of match fitness after his arrival from Corinthians on a loan deal until the end of the season.
Remy has been linked with a move to China, where the transfer window closes on 26 February, but Hiddink expects the Blues squad to remain intact.
"I think this squad we have now will stay until the end of the season," Hiddink said.
The Blues are unbeaten in 11 games and Hiddink is yet to lose in his 10 games in charge, but their hopes of UEFA Champions League qualification have receded with too many draws.
The Blues play in the last 16 first leg at Paris Saint-Germain next Wednesday morning (AEDT) and play Manchester City in the FA Cup next weekend.
Hiddink may make minor changes against Newcastle as a result.
"We might have some little options changed," he said.
