Head coach Mike Williamson said the centre-back trained fully today as the Blues prepare for Saturday’s home clash with Grimsby Town.
Thomas missed Williamson’s first game in charge at Swindon Town last weekend as he nursed a hamstring problem.
The new Blues boss said Thomas is available for Saturday but would consider carefully whether to throw the Saint Lucia international straight back into things.
“Yes, he’s fit for selection. He was involved in the full session today,” Williamson told the News & Star.
“We’ve got Saturday-Tuesday-Saturday-Tuesday [games coming up] – there’s loads of football.
“We’ve got to make sure he’s come through and he’s ticked the box, but we’ve also got to make sure that he’s feeling right and within himself – and we give him that opportunity, because we know what a big player he is, and he’s going to be for us.
“So it’s just about being smart about it, and not just throwing people in the first opportunity we get.”
United’s 2-0 win at Swindon could encourage Williamson to stick with the same defensive line and not rush 28-year-old Thomas back.
The Blues boss started Ben Barclay, Sam Lavelle and Jon Mellish as a central defensive three as United earned a welcome clean sheet at the County Ground.
Williamson, meanwhile, gave an update on Aaron Hayden, who is sidelined with a calf injury.
“He’s very close [to being] out on the grass now,” said the new Carlisle head coach.
“He’s starting to build up, so I think it’s going to be in terms of two to four weeks, hopefully, pending any little setbacks.
“He’s a big, strong lad, we’ve just got to make sure that we do things right, and be careful with him.”
Williamson said midfielders Ethan Robson and Taylor Charters were “dipping in and out” of today’s session as they continue their efforts towards a comeback from hamstring injuries in the coming weeks.
Another player back in the mix, meanwhile, is Jack Robinson, who returned to action in Tuesday’s 5-0 Central League Cup defeat to Blackburn Rovers.
The left-back had been out since April with an ankle injury.
“I think he definitely comes into our thinking, because he’s a good player,” said Williamson.
“He’s come back and he’s got loads of energy and enthusiasm, but again, we’ve just got to make sure that he gets his match sharpness and he’s ready, and we don’t throw him in too early.”
Williamson said Callum Guy, meanwhile, was today undergoing strength tests as he continues to build up his fitness after his recovery from an ACL injury.
The Blues boss said he hoped the midfielder would shortly be cleared to be back in full and “unrestricted” training, but added that his workload would still need to be managed.