“It's not the exact issue, it's a similar area, but it's not the exact same thing again,” Carrick said.
“And we're kind of still working through it a little bit to see how long the issue will be.
“We're hoping that it'll be soon, obviously, but at this moment it's still not quite clear.”
Sesko has been unavailable since coming off during Manchester United's League Cup defeat to Brighton on September 16. His latest setback has raised further questions about a problem that has disrupted his progress over recent months.
The Slovenia international had already missed international duty in March to rest his shin before aggravating the injury in United's 3-2 victory over Liverpool on May 3. He then spent three-and-a-half months out of action.
Carrick stressed that the current issue was not an exact recurrence of the original injury, although it affects a similar area.
Asked whether United could consider an operation, the manager confirmed that possibility had not been ruled out.
“Yeah, there are different things to look at,” he said.
“I think he recovered really well actually from the initial one, and there was a lot of time, and sometimes things get thrown up.
“The body does certain things and we've got to react to that and try and get him back as quick as we can.”
United are therefore still working through the available options rather than committing to a specific course of treatment. Carrick did not provide a firm return date, leaving Sesko's availability for the club's upcoming fixtures uncertain.
The forward is unlikely to be ready for the away matches against Atletico Madrid and Leeds next week, adding to United's selection concerns as they look to improve their results.
Sesko has scored twice this season, but his absence leaves Carrick without one of his attacking options at a time when United need greater consistency.
The manager has also called for more intensity from his players after a difficult opening to the Premier League campaign. United won only one of their first five league matches before the extended international break.
Carrick wants his team to show more aggression and urgency when they return to action, but first he must manage the injuries affecting his squad.
For Sesko, the immediate priority remains finding a solution to the shin problem. With the precise recovery timeline still unclear, United will have to wait before knowing when he can resume playing regularly.