The Wanderers' first-choice goalkeeper has been one of the club's most reliable performers since his arrival in Sydney's west last season.
The 31-year-old has registered a league-high 15 clean sheets over the past season and a half.
That form has led to Thomas securing a spot in Graham Arnold's Socceroos squad for the Asian Cup after more than two years in the international wilderness.
Lawrence Thomas has been a commanding presence for the Wanderers. (Mark Evans/AAP PHOTOS)
While Thomas will likely act as back-up to Australia captain Maty Ryan, Rudan will be forced to turn to one of two deputies to fill the void left by his first-choice No.1 over the next month and a half, starting with Monday's home clash against Macarthur.
Rudan has a choice between Daniel Margush, who hasn't started an ALM game since May 2022, and 20-year-old rookie Jack Gibson.
"We lose Lawrence for the next six or seven games but we just have to deal with it," Rudan said after last week's 2-0 loss to Wellington.
"It means an opportunity for the next one and we train and prepare them to be ready for it.
"It's not ideal for any coach, but you want to have the same XI as often as possible."
Already without Brandon Borrello until February, the Wanderers, who sit in third spot, will need to pick up wins if they are to close the gap on Melbourne Victory at the top of the table.
Rudan did, however, flag that creative linchpin Milos Ninkovic could be in contention to feature against Macarthur in what would be just his second ALM game of the season.
The Wanderers are unbeaten in their last four ALM games against the Bulls, who are coming off two consecutive losses and look set to be without Daniel De Silva due to injury.
