Middleton, who won the British GT4 championship in 2018, was set to take over from Imperiale Racing team-mate Alberto di Folco in the first of two one-hour Sprint Cup races but was clipped by the oncoming BMW M4 GT3 of Jens Klingmann which pulled into the box in front.
“The BMW was sort of on the limit [coming into the pits], trying to make up ground on us from the start,” Middleton told Autosport.
“He came in tight because they knew it was critical to stop as fast as possible, and there was just no space for me to get around and get access to the door.
“I tried jumping out of the way, but it was to no avail. It was a side glancing blow and knocked me over, so not ideal to say the least.
“I knew as soon as I was down, the pain was like nothing I’ve ever experienced before, it was awful. I thought I’d broken everything.”
Middleton was initially transported to the circuit’s medical centre before being transferred to the nearby hospital where the diagnosis was given.
“The doctors in Italy have said that it’s a fracture or break in my wrist, and in my right toe, there’s a fracture as well,” Middleton explained.
“My left leg, it got twisted and bent in a really bad way, but I managed to avoid snapping it. There is some damage to the tendons and ligaments, but it needs further checks to see what’s going on with it.”
He is back in the UK already and due to undergo a further MRI scan in his hometown of Newcastle later on Monday.
Di Folco, who had put the #6 Lamborghini Huracan on pole position, continued as a solo driver for the remainder of the race, finishing second on the road but incurring a one-minute sporting penalty as Middleton was unable to fulfil his second-driver duties.
However, di Folco took victory in the second race – for which Middleton qualified second on the grid the previous day – and dedicated his win to his stricken team-mate.
“[It’s] a beautiful victory that I want to dedicate to Stuart,” said di Folco after the race.
“Now, for me, the most important thing is to bring him the trophy and hope that he will be back in time for the next race.
“I was very motivated today, but it was not an easy race. The BMW was very fast, especially on the straights.
“Our car was still perfect, both in the wet and dry conditions and for this I want to thank the team.”
Middleton is competing in the Sprint Cup only this year and is hopeful of making a return to racing in time for the second round of the season, at Misano on the opening weekend of June.
“The doctors only went so far in their initial diagnosis, otherwise they would have had to keep me in further,” he said.
“They just had to patch me up and send me on my way.
“Hopefully I’ll be back for the next race, but we’ll see how things go with the scans. I’m already itching to get back in the car.”
