Main, who turns 19 next month, has impressed while on trial at Boro's Rockliffe Park training base and manager Tony Mowbray is interested in seeing what he can do at a higher level.
Mowbray has been carrying out his own assessment on the player along with his backroom team and they are ready to take a punt on the teenage forward.
Main also had a trial at Hartlepool United after his contract was paid up by the Quakers following his failure to break in to manager Mark Cooper's first-team plans.
The 18-year-old, born in South Shields, became Darlington's youngest ever player to play for them when he came off the bench against Peterborough in 2008 aged 15.
Aston Villa and Fulham have both previously been linked with the player, but it has emerged that Mowbray is seriously considering pulling off a deal.
Main's represntative, Tom Curle, of McHale Sports, said: "Curtis had signed for Middlesbrough and is absolutely delighted to get a chance to join such a good club.
"Curtis is now focused on working hard and proving himself at Middlesbrough."
Source: Northern Echo
Source: Northern Echo