Krystian Bielik was sent off against his former club as Charlton suffered yet another injury blow in their 2-1 defeat to 10-man Derby County.

Bielik, who was part of the Addicks’ promotion-winning campaign last season after joining on loan from Arsenal, was shown a straight red card for a reckless challenge on Conor Gallagher.

That incident arrived after 19-year-old Jason Knight grabbed his first-ever senior goal to edge Derby into the lead just 11 minutes into the clash at Pride Park.

Things went from bad to worse for Charlton when Macauley Bonne pulled up with an injury before being replaced at half-time with Lyle Taylor.

Knight then doubled Derby’s lead with his second-ever senior goal, only for a late Taylor penalty to set up a tense end to the decade.

Here are five things we learned…

Malicious or just mistimed?

Upon first viewing, Bielik’s red card looked very rash. He charged full-hearted into Gallagher following – in his own words – a “lazy” pass from Knight.

The referee Jeremy Simpson reached into his pocket for a red and, with few protests, Bielik solemnly walked down the players’ tunnel.

In that split-second moment it looked awful, however, replays suggest he got his timing wrong and was inches away from causing serious injury. Fortunately, there was no further damage.

READ: Charlton and Derby managers on Bielik's red card

A chastening experience

Despite being on the receiving end of a bad challenge, Derby fans quickly turned on Gallagher before taunting him and booing his every touch of the ball.

It appears many of them were unhappy with his reaction to the foul and deemed it to be overly excessive.

It ended up being a tough and bruising night for the on-loan Chelsea midfielder, and one he will need to learn from.

A baptism of fire

By the time the final whistle had been blown in Charlton’s 2-1 defeat to Derby County, the 11 players left on the pitch comprised a young average age of just 23 years old.

That includes five players aged 20 and under – Alfie Doughty, Albie Morgan, Ben Dempsey, Conor Gallagher and Josh Davison.

Usually, this situation would come about when managers choose to give their younger players some experience, but such is the situation at Charlton currently that Lee Bowyer was left with no other option.

READ: Charlton's top scorer out for a 'few weeks' in yet another injury blow

Who else to turn to?

Charlton’s rotten luck with injuries is no secret but that was brought into sharp focus once again.

At the end of their defeat to Derby County, a Sky Sports graphic showed they currently have 13 players out injured – which Bonne was added to in the same game.

The good news is that Chuks Aneke, Jonny Williams and Tomer Hemed are all out running again but, with Swansea City coming up tomorrow, it is too soon for any of them to make a return just yet.

Hobbling into the new decade

After victory over Bristol City, Bowyer appeared exasperated with how unfortunate Charlton have been with injuries – citing how the likes of Gallagher and Darren Pratley “did not come here to play every week”.

While circumstances tend to explain, and not necessarily excuse, performances, the Derby display outlined how decimated the side is by injuries.

Indeed, Charlton were second-best throughout and could have suffered a heavy defeat against 10 men had Derby been more clinical. However, one can only hope that key players come back sooner rather than later.