Gary Johnson admits he keeps his fingers firmly crossed whenever any of Bristol City's first team players are engaged on international duty.

And Bristol City's manager will once again be an anxious onlooker when Alvaro Saborio and Lewin Nyatanga put their bodies on the line in World Cup qualifiers tonight.

Striker Saborio is set to spearhead Costa Rica's attack as they bid to beat the United States in Washington DC and book their place at next year's finals in South Africa, while defender Nyatanga lines up for Wales against Liechtenstein in a Group Four tie at the Rheinepark Stadium in Vaduz.

Johnson will adopt a watching brief in Bristol, knowing that any injury sustained by either player could potentially rule them out of Saturday's Coca-Cola Championship showdown with newly-promoted Peterborough United at Ashton Gate.

"It's always a bit of a worry," claimed Johnson, who is already resigned to making do without Christian Ribeiro after the young defender suffered a recurrence of a groin injury while turning out for Wales in an Under-21 fixture against Bosnia and Herzegovina at Wrexham's Racecourse Ground last weekend.

"Of course, we are always delighted when our lads are recognised by their countries, because that helps raise the profile of our football club.

"But on the downside, there is always the risk one of them might pick up an injury and not be fit when they return to us.

"It's something we have become used to dealing with since we were promoted to the Championship and all I can do is sit back and wait to see how the lads get on.

"If Alvaro and Lewin come through their games unscathed, I'll be a relieved man."

Saborio's crowded schedule – he featured in Costa Rica's 4-0 win over Trinidad and Tobago in San Jose last Saturday – casts doubt over his availability for the Peterborough game.

The South American is not scheduled to return to Bristol until Friday and he will undoubtedly be tired after playing twice in the space of four days.

"It does create a problem for us," admitted Johnson. "Even if he gets through the game against the United States without being injured, he will still be tired after two games and lots of travelling.

"As for Lewin, he's only just come back from a serious illness and I'm not sure he is ready for three games in a week. He's already played 83 minutes against Finland, in Helsinki, and now faces a trip to Liechtenstein.

"As a club manager, there is nothing you can really do other than wait and hope for the best."

Johnson expressed concern when right-back Ribeiro was named in the Welsh Under-21 starting line-up to face Bosnia and Herzegovina last Saturday. The teenage defender lasted 52 minutes before limping off and being replaced by fellow Bristol City Academy product James Wilson.

Johnson revealed: "I told the manager (Brian Flynn) that Ribs was not properly fit, but they still started with him.

"He was out for almost a year with a ruptured cruciate ligament and has picked up a few niggles since coming back. He had this groin problem before he joined the Welsh squad and now it's been made worse."