The Addicks, who are currently one place above the relegation zone in the table, have been hit with injuries to a number of key players in recent weeks.
However, Hamer is confident that there is enough quality at The Valley to see the team turn things around.
"Character and spirit is what you need when you've got a thin squad," Sky Sports News quotes him as saying.
"We know we haven't got the highest budget in the league or the biggest squad but one thing we have got is a lot of team spirit and we've shown that over the last couple of years.
"We've just got to pull together. It's tough when your squad is thin, especially at the moment when we have key players out and we've got to pull together."
Charlton return to Championship action on Saturday when they face Blackburn Rovers at Ewood Park.