The 25-year-old, who signed following a successful trial in pre-season, scored his first goal for the club in the win against Salford City.
The versatile midfielder, who has worked with manager James Rowe before at Aldershot Town, has proved to be a shrewd addition.
But instead of cup glory Kellermann’s story could have been very different had he gone through with plans to hang up his boots after a couple of rotten years with injuries.
"In the summer I was thinking that is me done with football, I didn’t really have many options,” he told the DT.
"I was probably a week away from walking away.
"I have had a combination of injuries and bad luck.
"I was having discussions with family about what line of work I wanted to go down. It was a scary prospect. I am just happy I am not in that situation now.
"The manager text me to say come in and train with us and it just went from there. It has been a snowball effect.
“Everybody has setbacks but they were piling up for me over the years.
"It was tough but everybody in their life goes through things like that and it is about how you respond and what happens next and not getting too down.
"I am taking every day as it is and I know I am lucky to be in this position.
"I am feeling the best I have felt for a long time now.”
Kellermann has played a big part in Chesterfield’s rise to the top of the league and has fast become a fan favourite for his hard-working performances.
"It has been class,” he said of his time so far at the Blues.
"The manager and staff have been fantastic with me in helping get my body back to a stage where I can play week in, week out.
"The boys in the dressing room have welcomed me and I am just really happy at the moment.
"We have got a very humble dressing room. We believe we could be even further ahead in the league but we are not getting too disappointed or too high even though we are at the top and I think that is credit to everyone in there."
The former Aldershot Town and St Mirren man was loaned out to Tamworth at the start of the season to get some much-needed game time and he is reaping the benefits of that now.
"It was brilliant,” he said.
“I had double sessions so I was training with Chesterfield and training with Tamworth so sometimes I was going into games absolutely knackered which could have been frustrating for them but they were brilliant with me.
"They gave me everything I needed and I am really grateful to them.”
Kellermann supports Liverpool so he would love to face the Reds in the next round.
On his goal, he added: "I think it was overdue to be honest, I should have had a few already but I am happy to be off the mark.
"It was a proud moment and it will stay in the memory for a long time.
"It is a great day.”