The France international was heavily-linked with a move to Old Trafford earlier in the summer transfer window. However, the 26-year-old continued at the Spanish capital club's after the Court of Arbitration for Sport (Cas) upheld Atletico's Fifa transfer embargo.
United's chances of signing him before the start of the season suffered a further blow when Griezmann signed a new contract with Atletico in June. However, his buyout clause has been kept unchanged at €100m (£88.6m, $117.5m), which will come into effect from 1 January.
Olhats earlier admitted his former client would have completed a move to United, if Atletico were allowed to register players in the summer. He discovered him as a teenager and went on to represent him, before parting ways earlier in September. Griezmann's former representative stressed the former Real Sociedad man's situation at Wanda Metropolitano remains complicated.
"His situation is complicated, I know him well and he looks less efficient in the last few games, which means something," Olhats told French publication L'Equipe, as quoted by AS.
"I feel like he is feeling some form of fatigue. Everything can happen in football. Maybe he will change my mind in a few months, but I get the impression that this is the end of a story."
United have long been interested in completing Griezmann's signing as Jose Mourinho identified the Frenchman as a transfer target. The player himself admitted a move to Old Trafford in the future is a "possibility".
The Red Devils are not the only club interested in signing the player. Atletico's league rivals Barcelona are also in the race for Griezmann's signature after Ernesto Valverde made him the club's No 1 target, according to Mundo Deportivo.
The report claims the Catalan club have reached an agreement in principle with the player. Also, an opportunity to play alongside Lionel Messi, Luis Suarez and Andres Iniesta motivates the forward to make a switch to Camp Nou.
Should Griezmann decide to leave Atletico, either in January or next summer, he is likely to have top European clubs interested in his services. United and Barcelona are currently linked and the two giants are set for a transfer battle in securing Atletico star's signature.
Meanwhile, Griezmann ended his goal drought with a bicycle kick against AS Roma in the Champions League. Atletico won the match 2-0 at home and the Frenchman assisted Kevin Gameiro's goal in the final quarter of the match.