However, the Coventry boss admitted it was a move which probably suited both parties, with the striker growing increasingly frustrated with the amount of game time he was getting at the Championship outfit.
It also allowed the Sky Blues to free up finances and bring Swansea wing-back Jake Bidwell in on a long-term deal.
Walker made his Blues debut on Tuesday night, playing the full 90 minutes as Danny Cowley’s side drew 0-0 in the capital.
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His outing was only his sixth league start of the season as the 25-year-old sat behind Matt Godden, Martyn Waghorn and Viktor Gyokeres in the Coventry pecking order.
And it was that order of things which saw Walker grow ever more disappointed with his circumstances at the Coventry Building Society Arena.
With that in mind, Robins admitted it was probably best for the front man to leave – even though he wanted to retain his services over the second half of the season.
He told Coventry Live: ‘Tyler has been frustrated and wanted to play, and if I can’t get him in there then there’s no point him sitting around.
‘He needed to go and play, to get that frustration out of him and go and enjoy himself and go and score some goals.
‘Everyone wants to play and there are times when if everyone is at it and mentally ready to go into the side then you can carry four strikers.
‘And because of the games coming up they will get opportunities, there’s no two ways about it because you need to freshen up.
‘But as soon as you start to look beyond that and start to look disinterested or whatever – and this isn’t necessarily a criticism, just how circumstances are from time to time – you start to think: “I am not playing”, or “I want to play, I need to play”, and you start looking elsewhere.
‘The window is open and it becomes clear that you need to be playing.
‘You can keep hold of people and they become more disgruntled within the group, which isn’t great, and far from him being a problem in the building, he needed to go and be fresh; be fresh in his mind and his outlook, and be happy and score goals.
‘Life’s too short, and I said that to him. I said: “I don’t really want to let you go, want to keep you in, but I can see that you need to go and sort of bring yourself up a little bit and go and enjoy playing, and then we’ll see how things go”.’
Walker will remain at Pompey until the end of the season – a spell that sees the Blues navigate 21 more games before the final day of the campaign.
The striker’s Fratton Park stint could be extended further if a place in the play-off is secured.
Meanwhile, when asked if Walker’s Coventry exit could also go beyond this season and result in a permanent move away. Robins was remaining open-minded.
He added: ‘I think really we just let things unfold and see how things go.
‘Obviously I have to make things work as well. Within our model we have to make sure things work financially so we don’t go over the top and chase things, which we just can’t do.
‘We try to do things as incrementally as we can and do things as we go along, and if we can be flexible and nimble and try to make things work, then fine.
‘That’s basically my thinking behind the movements in the last week.’