Long has been constantly suffering from a hamstring injury, something the club managed to keep under wraps until Republic of Ireland boss Giovanni Trapattoni made it public during a press conference.
Long has still played a key role in the Baggies' impressive start to the season although the 25-year-old has not completed a full 90 minutes.
"There is an injury to Shane that everyone knows about now through circumstances we couldn't control," said Clarke.
"Playing through an injury is just a measure of how much they want to play for the club, which is great.
"They put their body on the line and play with little injuries - but we also have had great help from our medical staff.
"They go about their job quietly but play their full part as well in getting the players into a good place.
"The medical staff do all they can to make my job more difficult so I've got more options to choose from every week."