HITC Sport understands Preston and Wigan are eyeing the former Newcastle goalkeeper.
Alnwick has impressed at Port Vale since joining the club on a free transfer at the start of the season following his departure from Newcastle.
Alnwick came through Newcastle's youth academy and he made eight appearances for the first-team last season, but was not offered a new deal last summer.
The 22-year-old initially signed a short-term deal at Port Vale, but was rewarded with a two-and-a-half-year contract in October for his progress at Vale Park.
Alnwick has kept eight clean sheets in 31 games this season and his performances have alerted a number of clubs.
Preston are keeping tabs on Alnwick as they could be in the market for new goalkeeper once Sam Johnstone's loan spell from Manchester United ends this month and the goalkeeper has been linked with a possible move to Queens Park Rangers during this month’s transfer window.
Wigan are also admirers of Alnwick and could move for the keeper as they look to bolster their squad in a bid to win promotion back to the Championship.
Port Vale would be reluctant to lose Alnwick, but they are bracing themselves for interest in the former England youth international.