Reports in the UK have claimed the duo are aiming for a return from injury in April.
Speaking at a training camp in Dubai, Howe insists he won't be taking any risks with either player.
He told the club's official website: "I'd say they're on schedule from where they were given their respective injuries, but I wouldn't say necessarily ahead of schedule.
"They're both serious injuries, both enough to obviously be operated on and go through a very intense rehab period.
"Callum's injury, you have to be very careful with, that we don't push him back too quickly and he ends up injuring himself again because the Achilles/calf is a very delicate area of the body and you need to make sure it's robust enough to withstand heavy load.
"Kieran's is slightly different. [It's] a bone injury and I think, touch wood, if he can come through the early stages of coming out in his boots and then progressing quite quickly, he's one we could see back in action hopefully pretty soon.
"But with both injuries, I do think we have to be very cautious. We don't want to re-injure the player."
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