Athletic Bilbao coach Marcelo Bielsa feels it is unrealistic to expect his team to perform like they did at Old Trafford every week.
Athletic earned huge amounts of praise for their display in last week's Europa League last-16 first-leg encounter with Manchester United.
Most observers felt United were lucky to escape with just a 3-2 defeat that leaves them with an outside chance of turning the tie around tomorrow evening.
Yet Bielsa's team followed it by losing a crucial La Liga encounter with Osasuna, that leaves them in seventh place, an enormous 33 points adrift of leaders Real Madrid.
"The difference in points and finance is there for everyone to see," said the former Chile and Argentina coach.
"But I also believe that on one night or in one match a team like Athletic can get very close to the level of opponents such as Real Madrid, Barcelona or Manchester United.
"However, to maintain that throughout an entire league season is extremely difficult."
Bielsa is playing a cagey game with his team selection, although he did reveal midfielder Oscar de Marcos, one of last week's goalscorers, was doubtful after being struck down by a flu virus.
For all the significance of the potential achievement Bilbao could complete tomorrow, Bielsa is not getting carried away.
"There is no prestige to coaching a national side or beating Manchester United," he said, when asked whether victory would be the biggest moment of his career.
"Personal things like that do not concern me. They do not last very long.
"The evaluation of anything has to be done over the long-term, not the short. And we still have another very important 90 minutes ahead of us."