Summerville fired in an impressive hat-trick for the Under 23s against Crystal Palace on Monday night, as Marsch looked on from the stands.
Not for the first time in recent weeks, Marsch was impressed by the young Dutchman’s performance in Premier League 2 competition.
“I thought he played fantastic,” said the American.
“I think that he is doing a great job in the matches, showing that he is learning more and that he is more prepared and that we can count on him more and more.”
He added: “I think that he has grown since I have been here more and more and more.
“I have talked to him about his behaviour and mentality and professional behaviour every day off the pitch and what he needs to be like when he shows up here, what what the work week needs to look like and then how to adapt to the style of play that we want and how to continue learning the tactics and behaviours.
“And for me he has grown a lot in the last month and I think this performance is a representation of his professional behaviour, his work ethic, his mentality to try to learn and adapt.”
Check out the latest Premier League transfer speculation below...
1. Saints willing to sell trio
Southampton are reportedly “open to offers” for out-of-contract trio Theo Walcott, Moussa Djenepo and Nathan Redmond ahead of the summer transfer window. (The Athletic)
2. Hammers keen on Pickford
West Ham have reportedly entered the race to sign Everton goalkeeper Jordan Pickford in the summer. (Claret and Hugh)
3. Liverpool eye Sarr
Liverpool are still monitoring Watford winger Ismaila Sarr ahead of a potential move this summer. The Reds have made ‘surveys’ahead of a possible £40m raid. (Calciomercato)
4. Bowler in demand
Nottingham Forest are ready to make a fresh attempt to sign Blackpool winger Josh Bowler this summer. Burnley and Leicester City are also interested. (Football League World)
5. Magpies ‘will bid’ for St. Juste
Newcastle United are interested in Mainz defender Jeremiah St Juste, and it’s ‘quite possible’ they ‘will bid’ in the summer. West Ham are also being linked. (Fussball Transfers)
6. Hubers valuation revealed
Reported Leeds United target Timo Hubers could be sold for a “maximum” fee of just £5m by FC Koln this summer. (Bild)