The Hammers striker was dismissed for a second bookable offence after 63 minutes when referee Peter Walton adjudged him to be guilty of diving.
"I felt the defender made contact with Marlon," explained Pards after the game, "and I told the referee that I thought it was a foul.
"Even so the incident was certainly dubious enough not to warrant a booking for Marlon. I haven't seen it on video yet, but once I have then we will consider an appeal.
"It was certainly a major turning point in the game. We had got ourselves into a good position at 0-0, and were coping very well. We had set ourselves up to contain Millwall at the back and then hit them on the break with Marlon up front on his own and the two wide players, Matty Etherington and Luke Chadwick, supporting him.
"Marlon played the lone striker role well, and Matty, Luke and Nigel Reo-Coker caused them problems. Losing Marlon's presence was a massive blow, and it meant that I had to change the system, sacrificing Luke Chadwick who had played well. I felt that Matty just had a bit more energy to give us on the break, but unfortunately we couldn't break them down with a player missing.
"It was a really tight game between two good sides, and the sending off sadly just swung it in their favour."
Despite his disappointment at the 1-0 defeat, Pards insisted that he could not fault the effort of his players during a tense London derby.
"The commitment from the lads was excellent," said Alan. "It was a very tense game, as you would expect from a London derby, and there was a lot of stuff going on off the ball that made it tough for us.
"We were disappointed with the goal that we gave away and were upset at the sending-off, but I thought we dealt with everything that was going on during the game extremely well.
"There were players on both sides that lost their heads at times, but overall I thought the effort we put into the game was first class.
"I know the fans were frustrated at the end, and believe me I share that frustration. The team wanted nothing more than to give them a win today, and we're all desperately disappointed that we couldn't achieve that.
"Now we really have to pick ourselves up and focus our attention on getting back to winning ways at home to Watford on Saturday."
The Hammers cause was hardly helped by two major injury blows before and during the match, with Don Hutchison being withdrawn from the substitutes bench just before kick-off and Mauricio Taricco limping off after only 28 minutes with a hamstring injury.
"We are having a tough time with injuries just now," admitted Pards. "Don was suffering with a heavy bout of flu, and although he really wanted to take part, he was forced to pull out just before kick-off.
"Then Mauricio injured his hamstring and had to come off with only half an hour gone, which was a massive disappointment for him. Unfortunately, the hamstring can be a difficult area and he's now a doubt for Saturday's game.
"Darren Powell played well though on his West Ham debut. He trained with us for the first time the day before the game, and acquitted himself very well under difficult circumstances.
"It's definitely been a tough week for us, but there's no doubt that we have the ability and strength of mind to bounce back and start climbing the table again."