The striker came to West Ham in a club record fee of £45m in the summer of 2019 from Bundesliga outfit Eintracht Frankfurt.
Haller failed to live up to expectations in the English capital, West Ham moved him on to Dutch giants Ajax in January for £20m, taking a massive loss on the transfer.
Haller revealed he is frustrated at leaving West Ham prematurely having initially signed a five-year deal and explained he feels he left without finishing the task he took on.
The 26-year-old admitted that the weight of expectation on his shoulders was heavy owing to his big price tag, as he was under the scanner all the time during his West Ham stint
“I feel frustrated because it is like I left without finishing something”, Haller told talkSPORT.
“When people are talking about the price tag every day, they are waiting every day for something for this money.
“They expect even more from you than someone else.”
West Ham were unable to fill the vacant spot in their squad left by Haller with a new striker in the winter transfer window and could renew their hunt in the summer.
