The defender has not featured for the Hornets since August but his lack of gametime doesn’t appear to have affected his chances of earning a run out for Northern Ireland.
Cathcart’s only appearance of the campaign came against Brighton when he came off the bench but lasted just 19 minutes before he had to be replaced.
The 29-year-old sustained a knee injury and was due back in January but he suffered a setback and has remained on a recovery programme.
However, he is understood to be close to full fitness and O’Neill has drafted him into his squad for the friendly at home to South Korea on March 24.
Morecambe have no fresh injury concerns ahead of Tuesday's Sky Bet League Two home clash with Colchester.