Delap, who moved to Stamford Bridge from Ipswich Town in June, had also picked up a hamstring injury early on in the season and returned to the side only last month.
"He has been unlucky. We are also a bit unlucky because we need that kind of number nine," Maresca told reporters after the match.
"Unfortunately, he has already been out for two months, and he has to be out again. We don't know for how long, but it looks quite bad, his shoulder."
Chelsea, who played to their first goalless draw since a home clash with Crystal Palace in August, were left in fourth place in the league table with 25 points from their 15 games.
"I think it was a game where we lacked, and we missed a little bit of quality in the last third," Maresca said.
"For me, there were many mistakes. We missed some passes in the last third, some moments that we could shoot and didn’t."
Chelsea will next face Atalanta in a Champions League clash on Tuesday before hosting Everton on Saturday.
Check out the match report from Saturday's game with Flashscore.