Campbell, who played for Rovers in the early 2000s, died at the weekend while having a meal at a restaurant in Yarm, North Yorkshire.
Paramedics were called after he complained of feeling unwell but were unable to save his life.
A club spokesman said: “All at Doncaster Rovers are saddened to hear of the untimely death of our former striker Neil Campbell at the age of 45.
“Neil spent a little more than two years with Rovers after joining in a £10,000 move from Southend United.
“He netted 18 goals in 79 appearances as Rovers sought to battle their way back into the Football League.
“Middlesbrough-born Neil started his career with York City and also played for Scarborough and Barrow. We send our deepest condolences to all those close to Neil.”
As well as being a respected footballer, Neil was also described as a brilliant father to his two sons, with many who paid tribute noting his great sense of humour and kindness to others.
One of his friends said: "He was always horrible to play against on the pitch but great to have on your team and a true gentleman off the pitch. Heart of gold. Proper legend. Such a sad, sad loss."
Another touching tribute said: "RIP mate, you're truly with the footballing gods now."
The North East Ambulance Service said they dispatched a Medicar, a rapid response paramedic, a clinical manager, an ambulance crew, and a doctor to the scene. They received the call at 7.13pm on Saturday.
Police were also called to the scene.
A spokeswoman for the force said: "Police were contacted by ambulance service colleagues just before 8.10pm last night while they were treating a man who had become seriously unwell while out for a meal in Yarm.
"Officers attended and very sadly the man - who was in his 40s - was pronounced deceased shortly afterwards.
"A file will be prepared for the Coroner. All our thoughts are with the man’s family and friends at this difficult time."
The Middlesbrough-born striker also played for Scarborough, Southend United, Doncaster Rovers, Leigh RMI, Thornaby and Barrow during a career which began at York City.