The departure of Chris Powell as Addicks boss earlier this week following the club's FA Cup elimination against Sheffield United sent shockwaves through the south London club, but, after a second clean sheet and second successive point, Riga insisted it was onwards and upwards.
Ed Upson and Steve Morison went closest for the Lions but Ian Holloway's men failed to break the deadlock in a dull affair against their local rivals.
"My thought is that we physically were still feeling the effects of the game that we had at home on Wednesday," Riga said, referencing the midweek 0-0 draw against Huddersfield. "We had some difficulty with the game.
"In the first half we didn't have a lot of chances but we had a lot of corners, for example.
"In some moments we created some chances but the finishing was not there.
"I have seen my team all game in a good defensive collaboration. It was not easy all of the time but tried to create some opportunities.
"The result was logical, though of course I would prefer to win. Certainly for me our game in the week had an effect. I am not disappointed with the result and I am happy with the way that players showed that they would take something from Millwall.
"We have to manage all of the squad and we will do. As a coach I am always running recovering sessions and preparation ones so sometimes we want to do more to have more impact on the team, but that is hard when you are in our situation. We will adapt and we will get results."
On his first start for the club, Fred Onyedinma almost gave Millwall the lead after 17 minutes but he put his effort wide when well placed.
Seven minutes later and it was Charlton's turn to attack this time, with Callum Harriott eventually firing weakly at Millwall goalkeeper David Forde after getting into space.
Millwall could and should have taken the lead just before half-time, Upson hammering a 25-yard effort towards the bottom corner which Ben Hamer scrambled past a post and soon after the ball twice failing to drop for Steve Morison when in space eight yards out after a corner from the right.
Onyedinma broke well 10 minutes into the second half only to pull the ball back into empty space and Hamer appeared to take the ball out of his area as he slid along the ground to take the ball.
Morison fired a low cross in three minutes from time and giant Austrian substitute Stefan Maierhofer managed to miss the target when it looked easier to score.
Millwall have now not won in the Championship since January and, for all their attacking intent, the Lions rarely roared and Charlton enjoyed a fairly comfortable afternoon.
Holloway said: "My thoughts are the same as most of the people in here - all we needed was a goal.
"And I thought it was going to be a fairytale, young Fred (Onyedinma) when he whipped his head round that I thought 'here we go, go on son'.
"Unfortunately it went the wrong side. And they've come in and they're probably happier with it than I am because we wanted to push them and make them have to win two of those games.
"But you know I thought the crowd were excellent and I thought we kept trying. I thought there was a bit of nerves out there. We didn't create as many chances as we can.
"And that's very tough when you end up in a situation like we are in. You have got to be brave to play the way I want to. Hopefully I have simplified it for them."