On-loan Charlton striker Ade Azeez suffered a hamstring injury while playing for Wycombe on Tuesday night.
The Chairboys, who signed Azeez last month on a deal until January 1, 2013, are still waiting to discover the extent of the injury.
The 18-year-old was forced off after just 25 minutes of the Johnstone's Paint Trophy defeat at Yeovil.
It was Azeez's first start for Wycombe following two previous appearances as a substitute for the npower League Two club.
Smith, who was 75, had an association with United which lasted over 40 years.
He signed in 1959 and spent his entire playing career at Tannadice, making his final appearance in 1976. He was never booked in a career spanning 628 games, a statistic which ranks him fifth in United's all-time appearances chart.
He also played in the team which beat Barcelona home and away in 1966.
A statement on Dundee United's official website read: "As well as being a club legend, Doug Smith was a true gentleman, on and off the park, and highly respected and admired by all those who made his acquaintance.
"Our sympathies and thoughts are with his family and friends at this sad time, particularly David and Louise.
"The club flag is flying at half mast and Dundee United has approached the footballing authorities to request an appropriate mark of respect prior to kick-off on Sunday."
United play Dundee in the SPL at Dens Park on Sunday.
