Boston Red Sox owner John W. Henry insists the team did not want to trade star player Mookie Betts but feared the cost of his potential departure in free agency.

In the biggest trade of the MLB offseason, the Red Sox sent four-time All-Star Betts, David Price and cash considerations to the Los Angeles Dodgers in return for Alex Verdugo, Connor Wong and Jeter Downs.

Betts was the American League MVP in 2018 as Boston won the World Series, and his exit this month sparked outrage among fans.

But the 27-year-old is due to be an unrestricted free agent next year, and Henry says the Red Sox could not have run the risk of losing the player without getting his trade value.

The founder of Fenway Sports Group, which also owns Champions League winners Liverpool, compared the trade to that of Nomar Garciaparra in 2004 just months before Boston ended the Curse of the Bambino and won the World Series for the first time since 1918.

However, Henry also conceded he could understand fans being "disbelieving or angry or sad" as he would have felt similarly had the St Louis Cardinals - the team he supported as a child - traded Hall of Famer Stan Musial.

Starting a long message to fans, Henry wrote: "I would like to begin by addressing Red Sox fans directly about this offseason. We are used to challenging offseasons, but this one has been particularly challenging.

"So let me begin by saying that while they've been presented with extraordinary challenges this offseason, those of us sitting here today know that our baseball operations department under Chaim [Bloom] and Brian [O'Halloran]'s leadership has handled these challenges extremely well.

"We are confident and optimistic while at the same time cognisant of how all these challenges affect you, Red Sox fans."

He added of the Garciaparra trade: "All of us in the organisation hoped we could avoid ever having to go through something like that again. But most clubs face similar dilemmas from time to time.

"I understand there is probably little I can say today that will change how you feel about this, but it is my responsibility to try.

"The baseball organisations we compete against have become much more strategic and thoughtful about how and where they spend their resources in their quest for titles.

"We cannot shy away from tough decisions required to aggressively compete for World Series. This is what led to this trade."

Henry's statement concluded: "In today's game, there is a cost to losing a great player to free agency - one that cannot nearly be made up by the draft pick given. We have seen examples of this recently.

"We at the Red Sox will remember this as one of the toughest, one of the most difficult decisions we have ever had to make. We too love the young man, the great, great smile, the huge heart and the seemingly boundless talent he displayed here.

"We felt we could not sit on our hands and lose him next offseason without getting value in return to help us on our path forward.

"We carefully considered the alternative over the last year and made a decision when this opportunity presented itself to acquire substantial, young talent for the years ahead."

A tumultuous offseason is ending with Ron Roenicke as Boston's interim manager after title-winning manager Alex Cora left the team following the Houston Astros sign-stealing scandal.