I don't believe he brought him back and played him just to cup tie him. Given he couldn't have played against them even if he'd stayed with us, that makes no sense.
If you read O'Neill's reasoning behind the recall, it's all about being down to the bare bones due to a lack of signings. He spoke about one of the young defenders being a great prospect - there was absolutely no suggestion Welsh has a future at Celtic. 10 changes tonight doesn't suggest a lack of players, but their performance did scream a lack of quality.
O'Neill plays the bewildered pensioner, but he knows exactly what he's doing, and reading the Celtic fans reaction to the recall shows they got the message, loud and clear.