With Onana unavailable for the start of pre-season, United are keen to secure a new shot-stopper to bolster their squad, News.Az reports, citing talkSPORT.
Antwerp value Belgian U21 star Lammens at around £17million amid interest from the Premier League giants.
The 23-year-old once scored for Club Brugge against Real Madrid in a UEFA Youth League group stage match in the 2019/20 season.
A header from a corner, it sealed a 2-2 draw and sent his side into the knockout round play-offs.
Lammens spoke to Belgian outlet Gazet van Antwerpen earlier in the year about United's interest and how he'd suit the Premier League.
"The first time I heard I thought, 'Wow'," Lammens said.
"Immediately a world [renowned] team that follows you. That is special.
"Of course, I was also spoken to about it a lot and when I made a save in training, it was United this, United that [from colleagues]… It's only positive.
"Especially because it's the best competition in the world and my profile, my stature and way of playing, is similar to English football.
"You have to physically hold your own there and that suits me."
Onana's injury means he will miss pre-season, and potentially their opening Premier League match of the new season against Arsenal.
Altay Bayindir and Tom Heaton are United's two other senior options in goal.
They will then travel to the United States for the Premier League summer series to face West Ham, Bournemouth and Everton.
Fiorentina will visit Old Trafford on the weekend before the start of the 2025/26 campaign.
The fixtures will offer first outings for Matheus Cunha following his £62.5m move from Wolves.
