Vassell has managed just three appearances since the end of November due to a groin problem, which eventually needed surgery.
He went under the knife in February, but has now returned to training with a view to being back soon.
It would provide a timely boost as the Millers try and get over the Championship survival.
The 26-year-old was a key player in the opening part of the campaign, as playing in a wide position, his dynamism and directness caused opposition defences trouble.
His form was so good that he was called up to Northern Ireland squad for the autumn internationals and made his debut.
With the Millers having only Michael Smith as an experienced out-and-out striker Vassell's presence will be enjoyed by boss Paul Warne.
Warne said: “We'll have Kyle Vassell training with us this week which is good news.
“We only really have a couple missing now on the injury front.
“Sean Raggett has gone back to Norwich, so it is only really Jamie Proctor now missing.
“If Vass comes back that's great. Obviously it is different training with the lads than working with the fitness coach, so we'll see how he comes through this week.
“It might be an opportunity this weekend, it might not. We’ll have a good look at him this week.”
There is also an improvement at the other end as Clark Robertson should be available for the trip to Derby.
The former Aberdeen defender has missed the last two games with a hamstring injury, but will battle for his place against the Rams.
“Clark Robertson is coming along nicely, and he may be ready for the weekend,” Warne said.“We are virtually back to full strength which is great.
“Robbo has worked hard and is closing in on a return, so if he's back he can compete with Michael Ihiekwe and Richard Wood who have both done really well. We are going into the last part of the season in good fettle.”
The Millers will still be without new Wales cap Will Vaulks and Joe Mattock, who are serving respective three and two-match bans.