I am writing a description about player's performance and their participation in matches, but I am stuck in trying to find the right word for describing a player who has been participating in nearly every match for his team.
A very good option would be:
regular (Oxford Learner's Dictionary)
a person who often plays in a particular team, takes part in a particular television show, etc.
- We are missing six first-team regulars because of injury.
Some options would be
which technically means that they play at the beginning of a game, but if you called someone a "starter" most people (in AmE, at least) would assume you meant they played a large portion of the time in most of their team's games.
Ex: Who's playing QB for the Patriots this year? Tom Brady will be the starter, but Malcolm Mitchell might get some playing time at the end of some games to get him some experience.
a player who plays in all, or nearly all, of a team's games.
Ex: Since the Cubs infield is already full of great players, David Bote only gets occasionally playing time, but he could be an everyday player on many other teams.
1 : being a regular as distinguished from a substitute (as on a team)
Anecdotally, I've only heard this term used in reference to American football, but the definition from Mirriam-Webster seems to fit your need perfectly
A loyal, reliable, and hard-working supporter of or participant in an organization or team.
In British English, you might want to consider "Mainstay", the principle being that this player or players would be the foundation on which the team (comprising lesser or transient players) is built. The implication is solidity and longevity.
Celtic central defender Jack Hendry can become a mainstay for Scotland for the next decade, according to his club manager Brendan Rodgers.
The 22-year-old made his international debut in Tuesday's friendly victory over Hungary in Budapest.
"He has the quality to play for Celtic and the international team for the next 10 years," said Rodgers.
Try team player
someone who cares more about helping a group or team to succeed than about his or her individual success