Allen picked up the injury last week and, after getting a second opinion on the problem, turned up to his side's pre-season match against the Buffalo Bills yesterday on crutches.
The Colts went on to lose that match 44-20, and coach Chuck Pagano confirmed the injury news after the match.
"We're going to keep him off his feet, he's in a boot, he's on crutches," Pagano said.
"They don't want any weight on that foot for a couple of weeks. Nothing major. We expect to have him back sooner than later, and knowing Dwayne, he'll do the necessary things he has to do as far as treatment goes and staying off that thing."
Allen, who was the most prolific rookie tight end in the NFL last season with 45 catches for 521 yards, is expected to be fit for the opening match of the regular season on September 8.