Manager Nigel Worthington was critical of the fitness of his Northern Ireland players after seeing them beaten 2-0 at home by Hungary in a friendly.
"They need to do more work - it is as simple as that," said the NI boss.
"I cannot do anything, it is down to the players. Some of them are not getting regular games and they have got out of the mindset.
"They have got to go back to their clubs and do extra work because they are not fit enough."
Worthington was without a number of regular players but he did not use that as an excuse.
"There were still good enough players out there," he added.
"It is very disappointing. We did not get out of the blocks in the first half.
"The second half was a bit better but we conceded two poor goals.
"If we turn up in that condition and in that frame of mind we might just get a big disappointment in San Marino.
"It is the mental side and physical side of players that needs to improve.
"Some couldn't run or didn't run for whatever reason.
"There is a transfer window coming up in January and I thought it was a tremendous stage for some of them to put in a performance and there has not been too many who have done that."
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