James Beattie was so excited when we signed him never worked out even tho he tried hard ended up a flop
I still maintain that we always meant to sign Defour instead of Fellaini, were knocked back and decided "well, fine, we'll take the other one". Defour was the one we were rumoured with for a couple weeks before Fellaini just seemingly came out of nowhere....watching his first few games, I couldn’t understand why we signed Fellaini for big bucks but he was good.
Further back, I agree with @Joey66 that Henry Newton was a big disappointment. I’ll add Joe Harper and Tony Cottee.