The exciting conundrum facing Portsmouth boss John Mousinho as ex-Bristol City and Rotherham men vie for defensive role

And the head coach also detailed the reasons behind the 20-year-old’s withdrawal at half-time against Port Vale last week.

The January arrival has impressed significantly following his switch from Bristol City for an undisclosed fee.

Towler has featured in every game since his arrival, which has seen him impress in his 16 games to date - 15 of which coming from the start.

Meanwhile, Robertson recently returned from a groin injury, which had seen him out of action for almost three months.

But with both favouring a left-sided role at the heart of the defence and only one place to fill, Mousinho has revealed the challenge he faces with the pair now available

He told The News: ‘They’re players that are at different stages of their career.

‘Ryley is just coming into it, bursting onto the scene and is doing really well. Clark who is at the opposite end provides that experience, that know-how and has a really solid and excellent career behind him.

‘It’s a really good problem with both of them coming back into it.

‘Both have performed really well albeit in a short space of time for Clark on the pitch and I think everyone knows how outstanding Ryley has been.

‘I think how much he’s surpassed expectations for what we thought we could bring in January and how many games to play.

‘I’m almost certain if we bought him in January and he only played four or five games for Pompey then everyone would’ve been happy about that.

‘He’s gone way beyond that, performed really well and really happy to have both options for the weekend.’

After a difficult first half against Port Vale’s attack, which consisted of Ellis Harrison and Matty Taylor, the youngster was replaced by Robertson at the break.

And Mousinho has opened up on why he chose to withdraw the ex-Bristol City talent and hand the former Rotherham man his first league minutes since December.

He added: ‘One of the things Clark would give us was that real calmness in possession.

‘At half-time, we thought Port Vale would drop off in terms of energy level because they put so much into the first 45 minutes to take the lead and they were really good, energetic and caused us a lot of problems.

‘It dropped off in terms of (Ellis) Harrison and (Matty) Taylor not being able to sustain that and they came off after 65 minutes and by that time we had control of the game.

‘It was good to be able to get Clark on the pitch and both of them offer that calmness in possession but in a slightly different way so we thought the game would really suit Clark and thankfully it did.’