Arsene Wenger expects the future of Alexis Sanchez to be decided in the next 48 hours.
Sanchez is close to a £35million transfer to Manchester United and was left out of the squad as Arsenal lost 2-1 at Bournemouth.
Wenger admitted a move could be imminent but there will be no deal unless he can sign a replacement with United's Henrikh Mkhitaryan integral to any deal.
'Alexis would have played,' said Wenger. 'But it's a difficult period for him. He has always been committed until now but he could have moved yesterday, today or not.
'It will be decided in the next 48 hours. It was a bit difficult for him because he was on stand-by, a little bit. That's why I decided not to do it. He did not refuse to play.'
Mkhitaryan, signed from Borussia Dortmund for £30m in 2016, is greatly admired by Arsenal's new scout Sven Mislintat, who has joined the London club from Dortmund.
Arsenal are also among the clubs trying to sign Brazilian winger Malcolm from Bordeaux for £35m.
Wenger said there was 'nothing concrete' on Malcom but added: 'If Sanchez goes we need to replace him. We have to respond to it.
'Will he go or not? I don't know but at the moment. We're half in half out, you never know this kind of situation during the transfer period.
'I don't master the rhythm of that. It could happen today, tomorrow or not at all.
'That is why I decided to focus on the game. I didn't want to travel with him and suddenly find he goes somewhere.'
United are prepared to make Sanchez the Premier League's first £350,000-a-week player.
City have told Sanchez if he waits until the summer he would be able to pocket almost £70m in wages – double Arsenal's transfer valuation.
Sanchez's representatives are understood to have been told about Mourinho's superior offer.
Arsenal are prepared to let Sanchez leave this month, but want a fee of £35m. But the decision to leave him in London is likely to speed up the process of his exit.
United, who are prepared to sacrifice summer bids for Antoine Griezmann and Gareth Bale to fund a move for Sanchez, have shown a greater appetite to meet the Gunners' asking price, but Sanchez is said to prefer a move to City.
The financial package on offer at Old Trafford, however, will be tempting to the South American.
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