Southampton's season is back on track following a poor start to their campaign.
The former Barcelona and Holland international said:
"It is always possible to get into Europe, but we know it is very difficult because we know it is a gap of four or five points between us and Liverpool and West Ham. That makes it difficult, but if you win the last four then you have a better chance."
Eight wins and three draws in the Saints' last 14 league games has seen them climb to 8th in the table and just five points behind sixth placed West Ham United.
The South Coast outfit face already relegated Aston Villa tomorrow, before tough back-to-back fixtures against Manchester City and Tottenham Hotspur. They finish their season off with a home fixture against Crystal Palace, and will be hoping that there is something resting on that game.
Koeman claims his team have wasted big opportunities this season, especially away at Everton, and spoke of how he rues the points his side have thrown away:
"There is progress in the team and with individuals in the team, but I do believe we lost some big opportunities in several games - mostly away from home. That is the question why there is a gap between the teams above us. I already knew that after the draw against Everton, because that was a really big opportunity that we missed not to score and to stay more close to the teams above us."
The Dutchman will know that if his side do not pick up all three points at Villa Park tomorrow, their dreams of playing Europa League football next season will be all but over.