Gago suffered partial detachment of graft tissue in his right knee earlier this week, just days after returning to training following surgery last October to repair a torn anterior cruciate ligament, reports Xinhua news agency.
"I spoke with Fernando yesterday. He continues to want to be [at the World Cup] and he is fighting for that to happen," Sampaoli told a press conference on Thursday.
"I always stress the value that Gago has and that's why we are going to wait until the last moment."
Gago's career has been beset by a series of soft-tissue leg injuries. In addition to knee problems, the 31-year-old Boca Juniors star spent almost a full year on the sidelines in 2015 and 2016 after twice rupturing his left Achilles tendon.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)