The Red Devils drew 1-1 with Liverpool in the second leg of their Europa League last-16 clash at Old Trafford on Thursday night.
The 20-time English champions crashed out of Europe’s second-tier competition after a 3-1 aggregate defeat by Jurgen Klopp’s side.
Louis van Gaal’s side are off the pace in the race to secure a top-four finish after Manchester City moved four points clear of their rivals ahead of Sunday’s derby last weekend.
Former United captain Keane doesn’t believe the Red Devils will improve any time soon.
“It is a huge game. United need a response. We’ve not being seeing that. We didn’t see it tonight,” Keane told ITV Sport.
“There are troubled days ahead for United.”
Van Gaal is facing increased speculation surrounding his position amid reports Ryan Giggs or Jose Mourinho could replace the Dutchman at the end of the season.
The former Bayern Munich and Barcelona manager hasn’t won any silverware since he took over the reins at Old Trafford in May 2014.
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