United are embroiled in a six-way battle for Champions League qualification in the Premier League, while Atletico's FIFA-imposed transfer ban means they would not be able to bring in a replace were Griezmann to leave.
"We have to look deeper now because there is a lot more talk in England than there is in Spain," he told the La Liga Weekly podcast.
"As things stand, Atletico Madrid cannot sign a replacement so that surely must influence the decision. Although, if his buy-out clause is triggered there is nothing they can do about it.
"We have to look at where they finish this season as well, whether they finish outside of the Champions League spots - I don't think they will be.
"It's a big ask for Manchester United to try and qualify for the Champions League, I know that didn't deter Paul Pogba but I don't think it's cut and dried.
"We haven't heard much in Spain, where they tend to get their transfer speculation from the English papers in any case.
"It's going to be a talking point from now until the end of the season because the window is closed and people cannot cope without transfer news."
Atletico's struggles in La Liga this season, coupled with the subsequent uncertainty over Diego Simeone, has plunged Griezmann's long-term future into doubt.
The Frenchman cut a forlorn figure during Saturday's 2-0 victory over Leganes, choosing not to celebrate with team-mates after Fernando Torres converted the rebound from his saved first-half penalty.
But Gibson felt Griezmann's actions were a sign of a frustrated striker rather than an indication he was unhappy at Atleti.
"I saw two players moan when their teams scored a goal this weekend, and Griezmann was one of them," Gibson added.
"He was obviously annoyed he didn't score the penalty and thought he would snap up the rebound, but Torres got ahead of him and score it.
"There was a shrug of the shoulders, his arms were out stretched and a hissy fit from Griezmann.
"We have criticised Cristiano Ronaldo in the past for something similar so it's Griezmann's turn."
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