Real Madrid's Brazilian midfielder Kaka has revealed he thought he would never play again after undergoing knee surgery last summer.
The 28-year-old came on in Real's 3-2 league win over Getafe on Monday, his first appearance since Brazil's World Cup defeat by the Netherlands in July.
"At times, I was afraid when I thought about when I was going to come back or if I would," he told the club website.
"I must now earn a spot as the team's in great form."
Kaka, the winner of the 2007 Ballon d'Or, joined Madrid from AC Milan in June 2009 for 65 million euros, but has struggled to reproduce the form he showed for the Italian team.
Kaka admitted that, despite the encouragement and support of coach Jose Mourinho, his time on the sidelines had been a dark period.
"I've had some tough times and the things I've missed the most are the team get-togethers, training with my team-mates, being with them in the dressing room, playing before our supporters," he told the website.
"I lacked the joy I get from playing. I'm available now and I will do my best to play with joy again."
"A player feels very much alone when he is seriously injured and you go through it alone despite the help you get from others."
Kaka returns for the second half of the season to join a team who have progressed past the group stage of the Champions League, to face a two-legged tie against Lyon, and who lie second in the Spanish League, two points behind perennial rivals Barcelona.
He said he fully understood that he would have to earn his place in the team on merit now he was fit again, and was prepared to play wherever he was needed.
"It won't be a problem if I have to play closer to the goal. We'll have to wait and see how the coach builds the team. I have to earn a spot.
"The team is playing very well and competition is always very positive. The match against Getafe was hard, but what mattered in the end was winning."