But he is not alone, for the former Leeds United centre-back, who was unable to celebrate his 100th Owls start with victory on Saturday, is among a number of players at Hillsborough this term who have yet to reach their maximum.
“I have to do better,” he admitted. “I haven’t been as good as I have been in the last two seasons. It is as simple as that.
“If I look back on the last two seasons, I can’t remember doing too much wrong. These things happen in football. I have never seen a footballer, apart from top top-level players, who go through their career without a tough period.
“It is has not been my best patch of form at the moment, but no one is going to work harder to get out of it.”
On his milestone achievement, Lees, 25, added: “I’m very proud. It is a fantastic club. I can’t thank the club enough for what they have done for me.
“The fans have been great with me and I have loved it here. Now I just want to try and repay them for that support.
“At the moment, I’m just focused on trying to get back to my best form, help the team keep some clean sheets and move us up the table. I love it here and I’m very happy.”
Wednesday’s problems this season have largely been self-inflicted.
Too many times at Hillsborough they have started sluggishly, opting for possession football rather than beginning on the front foot and going for the jugular. Failing to score first has invited visiting teams to grow into the contest.
Before Brighton arrived in town, the previous three visitors to Hillsborough – Wigan, Bristol City and Nottingham Forest – had all taken advantage and netted first.
Only after conceding did Carlos Carvalhal’s side step-up their attacking intent, and each time they scrambled back to grab victory, papering over the defensive cracks.
It was a familiar start on Saturday, when Sam Baldock opened the scoring.
But Brighton are in a different class to Wigan, Bristol City and Forest, and with Lewis Dunk and Shane Duffy dominant at the back, the visitors repelled the Owls’ attempted fightback.
The hosts had enough shots over the 90 minutes, 25 to Brighton’s five, but the majority of those came as Wednesday chased the game.
Anthony Knockaert’s 73rd-minute goal in front of the Kop merely rubbed salt in the wounds as Brighton claimed a historic first win at Hillsborough.
Not even Gary Hooper’s stoppage-time goal could rescue Wednesday this time.
The Owls have lost twice at Hillsborough in six outings this term, as many home defeats as they suffered in the whole of last season.
“We weren’t good enough in all areas,” said Lees.
“We did have chances but we didn’t do enough to win the game.
“For us, it is disappointing as these are the games we need to be winning if we are going to do anything this season. I don’t think we can dress it up any other way. I think if we had played like we did against any team in the league we would have lost.”
Brighton took the game to Wednesday, but failed to test Keiren Westwood – Knockaert, Baldock and Jamie Murphy all firing wide –until Dunk played a stunning pass with the outside of his boot, which picked out Baldock on 27 minutes.
The striker nipped in behind Lees, and with Westwood rushing out, chipped the goalkeeper with the ball dipping under the crossbar.
It could have been 2-0 when Glenn Murray’s sweet volley was ruled out for offside.
Wednesday finally woke up and Adam Reach cut inside, only for David Stockdale to deny his low driven shot, before Jack Hunt’s follow-up was diverted.
The Owls right-back then picked out Fernando Forestieri, but his header drifted wide.
With Westwood staying off with a leg injury at half-time, Cameron Dawson, 21, was brought on for his debut.
Lees came close to an equaliser, but saw Oliver Norwood clear his header off the line.
Dawson could do little to deny Knockaert drilling home a second goal against the run of play on 73 minutes.
Wallace’s 25-yard strike was heading for the top corner, only for Stockdale to tip it over and Reach slipped in Steven Fletcher but the shot was deflected wide.
Then the unmarked Reach somehow blazed the ball over.
The Owls persevered and netted a stoppage-time consolation when Hooper fired home after Stockdale had thwarted Forestieri from close range.
Sheffield Wednesday: Westwood (Dawson 45), Hunt, Lees, Loovens, Pudil (Hooper 58), Wallace, Lee, Bannan, Reach, Forestieri, Fletcher. Unused substitutes: Jones, Palmer, Buckley, Sasso, Nuhiu.
Brighton: Stockdale, Bruno, Duffy, Dunk, Bong, Knockaert, Norwood, Sidwell, Murphy, Baldock (Skalak 76), Murray (Hemed 89). Unused substitutes: Maenpaa, Pocognoli, Goldson, Manu. Ince.
Referee: O Langford (West Midlands).