Championship leaders Wolverhampton Wanderers have been imperious all season long, running away with the division.
But Wolves suddenly find themselves without a win in three league games after draws with Preston and Norwich were followed up by a 2-0 defeat to fellow promotion hopefuls Fulham last time.
In that time the club's lead at the top has been cut to just six points.
Nuno Espirito Santo's side take on lowly Reading on Saturday before a tough run of games against the likes of Leeds United, Aston Villa and Middlesbrough.
"What we're seeing is that their levels have dropped off, I don't know, maybe 15-20 per cent," Goodman told Sky Sports Daily.
"Against, I would say, the large majority of teams in that division they'll get away with that and they'll win games of football.
"Against Fulham, who are absolutely flying, you can't get away with not being at your best and they were found out, there's no doubt about it.
"And I think this game on Saturday is massive for Wolves in terms of, they're playing against a team that are struggling, they have to regain that authority that they've got over that league.
"They are the best team in the league, they have been most of the season, every now and again they'll have a performance like that, against a good team like Fulham but it's how you recover from that.
"Saturday tea-time is a big game in terms of them re-establishing their authority."
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