Ricketts was due to undergo a medical this afternoon and Leeds are drawing up a three-year contract for the 25-year-old, who joined Boro from Bolton last year.
The striker could move as part of a swap deal for Mark Viduka. Viduka opened talks with Boro in Croatia this week.
Ricketts scored 37 times in 63 league starts for Bolton who paid Walsall £400k for him in July 2000 and Boro boss Steve McClaren then paid £2.5m to get him to The Riverside.
He has only managed 12 league starts, scoring four times, whilst at Boro but he has a huge amount of first division experience, and he scored 24 goals when Bolton were promoted to the Premiership in 2001.
Meanwhile, Sheffield United have signed Fulham striker Barry Hayles on a free transfer. Hayles signed a three-year deal at Bramall Lane after Fulham decided not to renew his contract.
The 32-year-old held talks with Leeds earlier this month and appeared favourites to sign him. Hayles scored 57 goals in 143 starts for Fulham.