The big-money arrival of Dutch ankle-nipper Marten de Roon meant that Forshaw was the assumed third-choice holding midfielder for Boro before the season began, but now his place in the pecking order is less sure.
His fellow Adam, Adam Clayton, has been equally impressive, and de Roon looked promising in his short time on the pitch before succumbing to injury against Stoke City on the opening weekend.
Little place for Leadbitter in starting eleven
There is, therefore, a clear top three for the holding midfield roles, and Leadbitter is not a part of it.
The arrival of versatile defender Calum Chambers on loan and the desire to give minutes to Julien de Sart - who could depart on loan - means that Leadbitter is somewhere between fourth and sixth choice in line for the position.
At 30 years of age, Leadbitter is not a spent force but he is past his peak. Boro fans know this; individually, he was better in the 2014/15 season than in the 2015/16 promotion campaign.
However, his influence is more than just his effect on and off the ball. The famous get-together at Casa de Leadbitter at a crucial point of last season helped get Boro's stuttering promotion push back on track after a tricky spell, and his walk to collect the Championship runners' up trophy, arm-in-arm with Karanka, proved that he is his manager's first lieutenant on the pitch.
As Karanka confirmed before the season began, Leadbitter is still the Boro captain and deservedly so. But, in his injury-enforced absence, other names are staking a claim to take the mantle in the future.
Downing, Friend, Gibson stake their claim
Golden boy Stewart Downing has worn the armband in the past, is the most experienced player at the club with international and European appearances to his name, and is closing in on his 250th league outing for the club.
Fan favourite and Teesside's favourite adopted son George Friend led his side out for their first Premier League match in seven years against Stoke and was one of the star performers on the day as he began his fifth season at the club.
When he too succumbed to injury, it fell to Ben Gibson, the young defender with Boro almost literally in his blood, to take the armband and he did so diligently, describing the experience as "what every Boro lad dreams of" on Twitter after the game.
The point should be made that the captaincy is a largely ceremonial role - a leader on the pitch will exert their influence regardless of an armband or lack thereof, and it is not merely a case of whoever's voice is the largest.
However, it is a role which is important to players and to the fans, and as such the decision should not be taken lightly.
The hierarchy at the moment appears to be Leadbitter, Friend and then Gibson. It is likely things will remain this way, and Friend will inherit the captaincy when Leadbitter steps down or Karanka decides to hand the role permanently to a first-team starter.
'Ben Gibson, he's one of our own'
Many Teessiders will want the sacred band to be draped around the arms of one of their own, and Gibson fits that bill more than any other.
Born within a few miles of the Riverside Stadium, nephew of chairman and patron saint Steve Gibson, graduate of the club's excellent youth academy and tipped as a future England international - Gibson has it all.
It wouldn't be a surprise. Karanka, a former centre-half like Gibson, is a huge fan. He recently told the Gazette that he hopes Gibson is at Boro "for the next 15 or 18 years and is with the national team".
Having been playing on loan at Tranmere Rovers just three years ago to the cusp of an international call-up, his rise from penalty-box liability to defensive cornerstone has been meteoric.
But there is such a thing as too much, too soon, and it is this which presents the greatest obstacle to Gibson. At 23, the majority of his career is ahead of him, and the captaincy will come to him some day. That much seems inevitable.
Beloved by all, Friend is the obvious choice
Most of the South Stand at the Riverside may beg to differ, but Karanka might just be George Friend's biggest admirer.
"He's a player who deserves every single thing," he told the Gazette recently. "You can see from the outside - he's the perfect son, the perfect husband, the perfect everything."
That is about the highest compliment any manager has ever paid one of his players, and there isn't a single Boro fan who would argue with him.
“For me committing to the Boro for another four years is because of so many things - a fantastic chairman, a brilliant manager and staff, great teammates, absolutely amazing fans and a beautiful area in which to live," Friend recently told the club's website.
Hard-working, passionate, talented, invested and likeable, Friend is the captain any Premier League club would be lucky to have.
When all the factors are considered, the 28-year-old is the obvious choice. If Ben Gibson does retire at Middlesbrough, George Friend will probably still be hanging around on the coaching staff to witness it.