Meanwhile, midfielder Ronny Vargas will have surgery on Wednesday to remove a screw from his reconstructed left ankle and flies out for Belgium next Monday.
Griffiths met with the off-contract Vargas on Monday and hopes to sign the Venezuelan marquee to a new deal before he departs.
“Ronny does have other options, but hopefully he feels like he has unfinished business here,” Griffiths said.
“The surgery is routine to remove a screw which he told me was restricting him in terms of power.
“With a three-month pre-season he will be bigger and better.”
Fellow South American attacker Pato Rodriguez, who arrived in January, appears unlikely to be offered a new contract.