Jurgen Klopp voiced fears over Jordan Henderson's fitness as a knee injury to Liverpool's captain took the shine off the manager's return to Borussia Dortmund.
Liverpool struck first in the Europa League quarter-final at Signal Iduna Park through Divock Origi's goal nine minutes before half-time.
But the club Klopp coached with distinction for seven years levelled through Mats Hummels' header early in the second-half and it remained 1-1 for next week's second leg at Anfield.
Henderson tried to continue after having treatment late in the first half but was replaced by Joe Allen at the interval due to a knee injury - potentially bad news for England boss Roy Hodgson as well as Klopp, with Euro 2016 on the horizon.
"We conceded a goal off a set-piece and that's not too necessary, but the disappointment overall is Hendo's injury," Klopp told BT Sport.
"He has a knee injury and that's not too good - it's really bad news. He will have a scan tomorrow."
Klopp was more upbeat about watching his side confound the doubters against the tournament favourites, as they displayed a defensive discipline rarely associated with their work this season.
"Dortmund is a pretty good side and everyone could see that but we had our moments and we could have won the game," he said.
"I'm pretty sure a lot of people thought we would lose two, three or 4-0. But we had some moments and around our goal we were brilliant. You have to work for these moments.
"We are not that far on our way like they are and we cannot at the moment play like they play, but we can defend and score goals so we can win."
The 48-year-old received an expected warm reception from the appreciative home faithful, while both sets of fans joined together in a stirring pre-match rendition of "You'll Never Walk Alone".
"Of course that was nice," Klopp added. "A lot of people spoke about it and thought about it. When I came on to the pitch it was respectful applause and that's nice. That's how it should be."