Boro interim head coach Steve Agnew was without goalkeeper Valdes for Monday's 2-1 defeat against Arsenal because of a rib injury and he has not recovered sufficiently to be involved at the Vitality Stadium on Saturday.
Brad Guzan will again deputise between the sticks while Agnew has also been left without skipper Leadbitter after the combative midfielder suffered a hamstring injury against the Gunners.
On his loss, Agnew said: "He is the captain and leader of the team and what Grant gives us is that leadership and the communication and the organisation, so yes of course Grant's a miss.
"I thought he was terrific the other night but when a player is injured then that gives an opportunity for another member of the squad."
Agnew will make late checks on striker Gestede, who is nursing a foot injury, and full-back Fabio, who damaged a knee on Monday evening, although he is hopeful both men will be available, as will Calum Chambers, who was ineligible to play against his parent club after shaking off a foot problem.
Boro sit six points from safety going into the Bournemouth game with as many matches remaining and Agnew knows they must start turning positive displays into points.
He added: "What we can do is continue to put the balls into dangerous areas and working on various ways to score a goal. That final touch is something we'd like to see more frequently.
"I was really, really pleased with the intensity [against Arsenal]. We remain confident going into the game at Bournemouth.
"They've done terrific but they'll see this as extra home advantage to get that extra three points to get that bit more security. I have no doubt this is going to be a really tough match but we're determined to get what we need."
Middlesbrough: Dimi, Guzan, Barragan, Fabio, Friend, Gibson, Espinosa, Ayala, Chambers, De Roon, Clayton, Forshaw, Guedioura, Downing, Stuani, Traore, Fischer, Ramirez, Negredo, Gestede, Bamford.