The tall and powerful Llorente, called up to the Spain squad for the first time in November, scored Athletic's second and his 10th of the season in a come from behind 3-2 league win over Malaga on Saturday to help move the club up to ninth in the standings.
His performance earned warm praise from coach Joaquin Caparros.
"Fernando has no limits and if anything he needs to be more ambitious with his shooting," Caparros told reporters.
"At the end of the match he was thinking about situations where he could have done something differently and that shows he is growing in stature as a player."
Caparros was under fire earlier in the season as Athletic slipped into the relegation places but has managed to fill his players with the sort of fighting spirit and self belief typical of gutsy Athletic sides down the years.
"It's been difficult but faith can move mountains," he said. "This team believes it can come from behind to win matches. We have to carry on like this and be ambitious."
Caparros said it will need a "titanic effort" to beat Sevilla, who he called "one of the top sides in our league and in Europe".
However, the Andalusians are reeling after they suffered a disappointing 1-0 defeat at Sporting Gijon on Sunday, their second straight loss in the league, to slip six points behind second-placed Real Madrid.
SAPPED MORALE
Uruguayan striker Ernesto Chevanton brushed off the disappointment, saying the players were confident of getting a good result against Athletic and beating city rivals Real Betis in the league next weekend.
"Now we need to look forward," he told reporters on Monday. "We have a tricky match against Athletic so we need a good result there and then we can turn our attention to the derby."
In Thursday's semi-final first leg, Real Mallorca travel to play runaway league leaders Barcelona at the Nou Camp after a morale-sapping 1-0 defeat at fellow-strugglers Osasuna which pushed them down to the bottom of the table.
Barca striker Thierry Henry said on Monday it was too early to start thinking about a Spanish league, King's Cup and Champions League treble, a feat never before achieved in Spain.
"We need to keep on fighting and looking forward," he said at a news conference. "Let's talk about what we have achieved at the end of the season." The semi-final return legs are in the first week of March and the final is on May 13 in Valencia.
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