The young Chelsea centre-back was called into the England senior setup by coach Gareth Southgate for the first time last week, after just six impressive starts in Frank Lampard’s exciting young Stamford Bridge side this season.
Tomori, who Lampard has rapidly promoted into his team after having the Chelsea academy product on loan with him at Derby last season, was well known to Southgate after 15 Under-21 appearances – but it was still a surprise call up.
Tomori, now 21, has been fast tracked into the Chelsea team by Lampard, who was prepared to let the highly experienced David Luiz leave in an £8million move to Arsenal at the start of the season to make room for the youngster.
But the Canadian-born defender, who has been with Chelsea since the age of eight, made his first mark at the club in unusual fashion back in February 2016 when he tangled with Costa.
He recalled: “I was still in school and I didn’t know I had done it in training.
“It was an accident. We both went up for a header and I had to flick the ball backwards and he tried to score. He headed the back of my head and he broke his nose.
“I didn’t know I had done it until the next day when it was all over the papers. I was getting a lot of messages like I meant to do it, but that was not the case.
“There was a lot of light hearted banter. I got back to school and people were asking about it. I was year 10 or 11. My mates had all seen it.”
And how did Diego, not known for keeping his temper, react?: “It was alright. He didn’t kick me in training.”
It has been a whirlwind week for Tomori, who played youth football for Canada and was being chased by Nigeria – for whom he also qualifies via his parents – but is now firmly in the England camp, with a Champions League debut swiftly followed by news of his first senior call up.
He said: “It’s been a good week. Nice to get the England call-up, winning in Lille in the Champions League and then beating Southampton on Sunday.
“The manager told me I had been called up after the Lille game so I had to keep it a secret. I told my family and then it got announced on Thursday.
“I had no idea it was coming. The manager told me and I was like ‘oh’. It was a nice feeling.
“I’m committed to England now. I was waiting for a call-up because the last international break I didn’t get one from anyone. This international break, I was waiting and England called me up.
“It wasn’t England all the way. I had certain people and certain things that I had to consider. I spoke to my family and people that I care about about it and that’s the decision I came to. So when England came calling, it was difficult to say no.
“England is obviously such a big nation, as are Nigeria and Canada. I was going to be happy with whoever called me up but it’s nice it is England.”
It did though arrive quicker than expected: “Yes. It was just a case of giving my best for my club week in, week out and try to get in the squad. It’s a mad turnaround.”
Lampard has insisted that Tomori is now in his top two centre-backs. The youngster said: “Having the manager say that about you, that’s what you want. I know he has that faith in me and he’s showed me that.
“I knew I would have to take myself up a couple of levels this season. I wasn’t expecting to be in the side. I came in trying to improve and give myself the best chance.”