Yoro, 19, is yet to make his competitive debut for the 20-time English champions, having suffered a fractured metatarsal during a pre-season friendly with Arsenal towards the end of July.
The centre-back has been back in training since the early stages of November, and it had been thought that he would be in the squad against Ipswich Town in the Premier League on Sunday afternoon.
Yoro did not make the trip to Portman Road, though, and he was also absent from training on Wednesday, with the team preparing for Thursday's Europa League game with Bodo/Glimt.
Amorim has said that the Frenchman "is available to train", but the club are bering careful when it comes to the teenager due to the risk which comes with bringing him back sooner than he is ready.
Yoro will not be involved against Bodo/Glimt on Thursday
"He is available to train, but we are working on his fitness. This is important. He is a young guy, this is a massive club. It's very important the first image, so we will try to put it together because he's a great talent," Amorim told reporters.
"We believe a lot in him, and we are trying to prepare the best way to start with Leny."
Yoro made 60 appearances for Lille during his time with the French giants, and he had widely been expected to make the move to Real Madrid during the summer transfer window, but Man United won the race for his signature.
When fit, Yoro is expected to be used as the right-sided centre-back in a back three, while Matthijs de Ligt and Lisandro Martinez are also likely to be in Amorim's first-choice defence.
Are Martinez, Maguire both now available?
Martinez and Harry Maguire both trained on Wednesday, with the pair handing Man United a double fitness boost.
Amorim has revealed that Martinez, who missed out against Ipswich on Sunday with a back problem, is available against Bodo/Glimt, but Maguire is not yet ready to return.
"Not Harry. Licha is ready. He didn't stop [playing for] too much time, so I feel he is ready. It is a different situation with Harry, we need them both, but they are in a different situation. They are both training, Harry soon will be on the pitch also," said Amorim.
Maguire has only made nine appearances for Man United this season, with the Englishman sidelined since the start of October.
Victor Lindelof was also missing against Ipswich, with the Swede picking up a groin problem while on international duty, and it is unclear whether the experienced centre-back will be back in the squad against Bodo/Glimt.