The midfielder's season is over due to injury.
"Last season was tough for him," said the Uruguayan. "Being so small, it took him time to adapt to English football and the system I played didn't really suit him.
"He then had a difficult summer after not making the World Cup squad but he didn't sulk. But when we returned before the season he was a different player - like a new signing - and we were looking to use him in different positions.
"So losing him is a big blow. You need to know him as a person, how nice he is and how determined he was to make an impact this season after what happened last year."
Poyet added: "He can still make a big impact at this club when he's fit. If he comes back next season in the way he started this one, he is going to play regularly."