Ronald Koeman's team host the defending Premier League champions at St. Mary's this weekend, before travelling to Bournemouth next Tuesday and hosting relegation strugglers Sunderland the following Sunday.
A run of six league matches without defeat, during which the Saints have incredibly not conceded a single goal, has lifted the South Coast club to sixth in the table, just a point behind Manchester United and seven points off a Champions League spot.
Ward-Prowse believes that by the time the upcoming three-match spell is over, the club will know whether they are serious European challengers or not.
He told the club's website: "I think we could look back on it at the end of the season and it could be a defining period for us. We've got to make sure that we're professional, we recover right and make sure that we're ready to go again.
"I know all the lads and the management staff, we're all wanting to get the club back into Europe and I think these three games could be pivotal towards that."
Meanwhile, Saints goalkeeper Fraser Forster seems to share his teammates opinion on the importance of the upcoming run as he tweeted a picture on Tuesday of his preparations.
The former Celtic man, who returned to action last month after 10 months out of action, wrote on his official account: "Good training session today ahead of a big week. #wemarchon."
Southampton have been a consistent top half side for the last couple of years, finishing eighth and seventh in 2014 and 2015 respectively.
However, they have not finished as high as their current position in the top flight of English football in over 30 years, last finishing in the top six in 1985.