McIlroy's title defence and keenly anticipated contest against Spieth was thrown into doubt on Monday when the Northern Irishman revealed he had ruptured an ankle ligament while playing football with friends.
While many observers believe McIlroy is certain to miss the third major of the season, the American winner of this year's U.S. Masters and U.S. Open is keen to see the world number one recover in time to play at St Andrews next week.
"It kind of dampens it. You want the defending champion, much less the best player in the world at the event," Spieth told the Golf Channel when asked about the 26-year-old's injury.
"You want all fields to be full strength no matter who it is. Losing the number one player in the world for a major championship would be tough."
McIlroy has said that he would undergo further testing in the next 48 hours and not rush into a decision about his participation at the British Open.
The 21-year-old Spieth is ranked just behind McIlroy at number two in the world and thinks that the injury "was really unfortunate".
"Accidents happen and I just wish for a speedy recovery. We all want him back as soon as possible," the Texan said, adding that McIlroy's absence would not make winning the tournament any easier.
"It's still just as challenging," he said. "It's still a major championship and there is a lot of unbelievable talent. I obviously wish he was there."
(Writing by Douglas Beattie; Editing by John O'Brien)
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