The winger has now returned to Liverpool for initial treatment after having what has been described a minor procedure.
It's understood that [Boro](https://www.thenorthernecho.co.uk/sport/football/middlesbrough/) boss Michael Carrick has not ruled out the possibility of Doak playing again this season.
But at the very minimum the 19-year-old now looks set to miss a large chunk of Boro's remaining 11 Championship games.
Doak last played for Boro in the 2-1 defeat at Preston in January. He then suffered a thigh injury in training ahead of the Tees-Wear derby against Sunderland and has missed the last six Championship games.
Boro were initially hoping Doak would be able to return in early March but the injury turned out to be more serious than initially anticipated, with the decision made that minor surgery was the best course of action.
The Scotland international is now back with his parent club but Boro and Liverpool will remain in close contact over the course of the coming weeks.
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The setback is a major blow for Boro, with Doak having dazzled in the first half of the season after joining on loan in the summer.
The 19-year-old has scored three goals and registered seven assists in his 24 Championship outings for Boro, with his form at the Riverside prompting Premier League clubs Ipswich and Crystal Palace to lodge permanent bids in the January transfer window.
Those offers were rejected by Liverpool, who have high hopes for Doak in the future and have been thrilled by how his loan move on Teesside has played out.
Doak has also established himself as a senior Scotland international this season but his latest setback means he'll miss the crucial Nations League play-off ties against Greece later this month.
Carrick has repeatedly praised Doak throughout the season.
He said at the end of last year: "He’s got really good enthusiasm for playing. That comes through in the way he plays. He’s always looking to be so positive and direct.
"To have that kind of purpose about your work is so valuable. You see it in the energy and the willingness to keep trying things. It’s a real joy to see, and quite refreshing, really."
After Doak starred in Boro's win over West Brom in January, Baggies boss Tony Mowbray said: "What is Ben Doak worth now? What was he worth before he came here and what's he worth now? It's huge credit to the football club that he's been given the license to go and do what he does.
"Every game I've watched he's probably been their most productive player. "He's a special talent. He's a good footballer."
Despite the blow of Doak's fresh setback, Boro aren't short of options on the right side of their attack. They won the battle to sign Morgan Whittaker in January and the 24-year-old has quickly settled, while Marcus Forss has also returned to the side in the last two games and impressed in the win at Stoke.