Mr Spray died in Sofia on October 14 after travelling with friends to watch England play Bulgaria in a Euro 2020 qualifier.
The 32-year-old, from Heath Hayes in Cannock, was said to have been found in the centre of the city.
Bulgarian authorities claim Mr Spray was in a "helpless condition" and was taken to hospital before police were called when he began behaving aggressively.
But his family said that he died in transit with police although the circumstances are unclear.
Mr Spray’s parents Jillian and Malcolm – who is suffering from prostate cancer – have been invited to attend Albion’s home game with Barnsley tonight as guests of the club.
His sister Katie has also been invited to attend along with other family members.
Albion will provide a signed shirt which his friends will take to his seat at the back of the Birmingham Road End.
There will also be a full tribute in the match-day programme.
"My dad rang me to say that Rob was died. The worst phone call I have ever had," Katie said.
A Staffordshire Police liaison officer has been working with the family but Bulgarian police are yet to provide more details.
Mr Spray's sister said the matter had now been raised with both the UK and Bulgarian ambassadors.
Katie added: "We have had no answers at all and he has been dead over a week."
Around £25,000 has been raised through an online fundraiser set up by friends to help his family.
His sister told Radio WM that the family will look to employ a private investigator to get the answers they need.
"Obviously if we don't get any more answers then me and my family want a private investigator or a solicitor out in Bulgaria which we have been told to get," his sister said.
Katie said she was one of the thousands of Thomas Cook employees to lose her job last month and the family are worried about paying for any investigation.
"We don't know anything at all. We have been told there are 10 witness statements in Bulgaria but obviously they will need to be translated," she added.
"There's CCTV footage in the hospital but that hasn't been released to our police yet."
She added: "He is not a football hooligan my brother. He loves football. He is not aggressive."
Mr Spray travelled out with friend Andrew McMath who was celebrating his 30th birthday.
He said the last time he saw Mr Spray was in the morning on the day he died.
He told how he saw Rob walking down two flights of stairs in a "fine condition".
"When someone leaves at 9am you expect them to go for some cigarettes or a McDonald's or something like that," he told Radio WM.
"You expect them to come back. It's broad daylight at 9am. There shouldn't be any issues going out at that time of the morning."
Rob's friends tried calling him after he had been gone for a while and his phone had dropped off a tracking app.
They spotted an announcement on Twitter saying that a 32-year-old man had been taken to hospital.
Mr McMath tried to get information from officials but later he had a phone call from Mr Spray's sister to inform him of the tragic news.
More than 10,000 have signed a petition calling for the Foreign Office to intervene and hold an investigation.
A spokesman for the Foreign and Commonwealth Office previously said: "We are supporting the family of a British man who died following an incident in Sofia, and our staff are in contact with the UK and Bulgarian authorities."