Goalkeeper Dúbravka and centre back Schär were both withdrawn from international duty with Slovakia and Switzerland respectively over the last fortnight, while midfielder Shelvey missed the defeats at Chelsea and Everton just before the break.
But head coach Howe says that all three could be involved at the Tottenham Hotspur Stadium this weekend as he seeks a response from his charges after last month's back-to-back losses.
"Fabian came back having not played and not trained, but we've had a couple of sessions with him so we think he'll be fit," he said.
"Martin trained with us for the first time yesterday, so we hope he'll be fine.
"We've got a little bit of illness in the camp, probably like most teams have around the country, but we've still got a couple of days before the game so we hope everyone will be OK.
"Jonjo has trained – he hasn't trained every session we've done, I think he had a bad bout of illness – but we hope he'll be OK."
Two other first team regulars, meanwhile, are continuing to work towards a return to fitness, with full back Kieran Trippier set for a scan on the foot injury which has kept him out since he netted the winner in the 1-0 victory over Aston Villa in February.
Leading goalscorer Callum Wilson, who is yet to feature in 2022, is also working on a comeback from injury but Howe believes his most immediate decision to make centres on his midfield, where Joelinton, Bruno Guimarães, Sean Longstaff, Joe Willock and Shelvey are all competing for a place.
"It's a great position for me to be in," said Howe. "That midfield area has been the key area for us I think – it's been one of the strengths of the team, without a doubt.
"I think we've had a really good mix in there of technical quality, physical attributes, and defensively I think they've been very, very good. It's a nice problem for me to have. I've got to try and pick three out of those five if everyone's fit and we decide to play with three."
Late goals from Kai Havertz and Alex Iwobi saw United beaten at Stamford Bridge and Goodison Park in March and Howe – who saw some encouraging signs in both matches – says his side must get things right tactically if they're to return from north London with three points.
"I think the two games we had have been very different but the same outcome – narrow 1-0 defeats very late in the game," he said. "It's been a difficult one to take – both games have been very difficult to take, because we felt we had given a lot.
"In the Chelsea game, defensively we were excellent, and it was a very frustrating feeling. In the Everton game, in the first half we were excellent, in the second half I think we fell away from those high levels.
"Now we need to regroup and go again in what is a very difficult game against an in-form team. It's a really tough game, this one, and I think tactically we need to be very good. Antonio Conte's teams are very well set up and they've got outstanding players."
