The former Genesis star, 66, tripped in his London hotel room during a visit to the toilet in the middle of Wednesday night, hours after he performed at the Royal Albert Hall as part of his comeback tour.
Collins suffers from a “drop foot” as a result of a back operation which causes him difficulty walking.
He was rushed to hospital, where he was given stitches for the cut on his head and will be kept under observation for 24 hours.
His scheduled Thursday and Friday concerts at the venue have been postponed until November and he is expected to continue his comeback tour in Cologne, Germany, on Sunday before performing at British Summer Time Hyde Park on June 30.
His management said he was “recovering well”.
“He rose in the middle of the night to go to the toilet and slipped in his hotel room, hitting his head in the fall on a chair,” they said.
“Phil sends his sincere apologies and thanks to fans.”
The In The Air Tonight and Another Day In Paradise star officially retired in 2002, but announced his return in October last year.
His two remaining Royal Albert concerts will now take place on November 26 and 27 with all tickets for both remaining valid, they added.